As written elsewhere, I'm a firm believer in the training qualities of pre Searing and "the road to Lion's Arch" as I like to call it.
But what profession should you do this on? Here's a list in the order I think they should be experienced, and why.Note to advanced players: The analysis of each profession and the order I put them in sometimes contradict established wisdom (eg. "warrior does not pay attention to the team" or "ele does great damage"). That's because this is about newbs doing newb things in beginner areas. This is about stuff that the game will teach them "against their will", so to speak, while they still don't know anything about it.
Note to beginners: Each profession includes a list of checkpoints, things you're suppose to take in while using the character. Keep an eye on the list as you go along, see what you do fine and what you feel needs more work.
What secondary profession should you take? Take Monk. Period. "Yes but secondary X offers..." No. Monk will give you self heals and a reusable ressurect skill. They're actually mostly useless, but you'll learn that later. In the beginning, they will make you feel good about yourself and you will wean yourself off the monk skills naturally, over time. Which will allow you to focus on the primary profession. (As for Monk, take Warrior for secondary. I will explain why below.)
What Prophecies areas this guide applies to:
Quote: Originally Posted by Urcscumug Pre Searing and the zones before Lion's Arch have been designed as a training area which will teach you GW very very well. So start in Proph and work you way to LA if you want to learn GW well, at a slow and decent pace.
Explore Pre-Searing fully; meaning doing all the quests, getting all the quest rewards, try out secondary skills and ideally suceed to make at least one full Northlands hunt (kill all the Charr). It's ok if for Northlands you team up with another higher level player, as long as they explain how they do it and make you help, not just drag you along.
Go to Post whenever you finish all that, regardless of level. Don't stress too much, you should be done with Pre in a few days the first time and gradually work your way to mere hours.
When in Post, start exploring Old Ascalon, including Regent Valley, Pockmark Flats and Eastern Frontier, then work your way on foot through The Breach, Diessa Lowlands (with a side trip to Flame Temple Corridor and Dragon Gullet), Ascalon Foothills, Traveler's Vale, Iron Horse Mine, Anvil Rock, Deldrimor Bowl, Griffon's Mouth, Scoundrel's Rise and North Kryta Province, unlocking all outposts on the way and doing all the quests. You will get tons of useful skills and items for nothing, you will level to 20 smoothly, you will uncover 30-50% of the Tyrian map, get some decent pocket change, you will meet crafters and collectors that will upgrade your armor and weapons as the zone requires, meet "hidden" skill vendors that offer unique skills, and you will learn a lot about the game. I also recommend doing the mission that takes you to a certain outpost only after you've reached that outpost on foot. Other quick notes:
* I covered core professions only, since I don't think Nightfall or Factions are suitable for a beginner. But feel free to add arguments otherwise and opinions on the suitability of non-cores for teaching.
* I only take into account the zones before LA, with all their limitations (skills, items etc.)
* It's mostly about using henchmen. If playing with human players, consider taking up places from the profession list in increasing order (ie. 1 player = W, 2 players = W+E, 3 players: W+E+R, 4 players W+E+R+M etc.) Fill the empty places with appropriate henchies.
* Please keep the terminology accessible, since this thread is intended for the newbies.
WHAT PROFESSIONS YOU SHOULD TAKE AS A NEWBIE, IN THIS ORDER:
1. Warrior
The warrior is about jumping in and physically laying as much hurt as possible at point blank range. It's a simple enough concept that you can take it and dive right in. It doesn't require that you pay much attention to what the rest of the team is doing. Go on, grab a piece of metal and start waving it around.
What being a warrior will teach you:
* How your armor and shield protects you (armor rating). Conditional mod effects.
* How you do damage (weapons, attack rate). Also, weapon mods and armor penetration.
* Using collectors and weapon/armor crafters.
* The basics of using skill combos.
* The basics of using skills that modify your abilities (stances, shouts).
* About the aggro buble and the compass. In time, keeping the corner of one eye on the compass becomes second nature, like the rear view mirrors while driving; you don't actually stare at it, but you are constantly aware of the red dots and your aggro.
* How the foes tend to move during battle and react to your attack.
* Pulling smaller groups with longbow or flatbow, instead of fighting large groups all at once.
* How the rest of your team will follow your lead and focus on the same mob you target. Calling targets.
* Spiking: everybody focusing on the same foe to take it down before the others can do much.
* Target priority: starting the attack with certain members of the enemy groups is better than with others.
* Physically controlling the battle field by body blocking and by forcing foes to turn on you instead of your mates.
* Not to overextend (straying TOO far from the team).
* Minimal caring about your team, in the form of noticing when a mate is in bad trouble and leaving your current adversary to go help them.
* Minimal team support, in the form of shouts (such as "Watch Yourself!").
2. Elementalist
Like the warrior, the ele is about laying the hurt on the enemy. But they go about it indirectly, via spells. Doing it effectively requires a little more thinking than simply jumping in with a piece of metal.
What the ele teaches you:
* Since the attacks are indirect and delayed, you will have to start predicting what the foes do and where they will go next.
* The basics of energy management. It's your basic fuel, but it tends to run out so you have to learn how to use it wisely (cheaper spells, energy-saving skills).
* The various areas of effect (radius of damage around the point you applied the spell).
* Considering single-target vs multiple-target damage.
* Increased battlefield control via snares.
* The basics of maintaining enchantments (on yourself).
* More advanced skill combos.
* The basics of using stuff that inconveniences the enemy (conditions, hexes).
* The basics of positioning during battle.
* Keeping an eye on one team member (on what your warrior does).
* What to do when the foes go around the warrior and come for you. Kiting (running around until someone takes them off your back) and self-protection spells.
* Team support with Earth Magic wards.
3. Ranger
After the warrior and the ele, with the ranger it will be the 1st time you won't feel like the lead singer on the band anymore. The ranger is a combination of attack and support character. But it's a bit of a lone wolf so you still won't have to pay much attention to the team. You will spend your time a bit of a distance away from the main team, having a vulture's view of the battle field, picking off targets with your arrows, and taking care of your pet.
What using the ranger will teach you:
* Using bows and projectile attacks. When some bows are better than others. Bow fire rate.
* The advantages of a good position. You need line of sight, and you benefit from altitude above the enemy.
* The basics of using weapon damage modifiers (preparations).
* If playing with a human team leader, the basics of following target calling (press T and start attacking).
* Having a pet will teach you to pay attention and take care of one team member at all times. You will keep an eye on what the pet does, heal them, resurrect them, command them.
* Like the ele, you can inflict conditions on the enemy.
* More advanced energy management, with more skills dedicated to it, and an entire attribute line.
* You can provide support with traps and spirits.
* The basics of putting pressure on foes (harassing them with damage/conditions so they can't do their job).
* The basics of interrupting enemy skills. What bow works best (recurve). Spotting skills you can interrupt and doing so.
* The pros and cons of always finding yourself a distance from the rest of the team.
* The distance and position often offer you a good view of the entire battle field. It will teach you to watch the field at a "macro" level and to make quick judgements about how things are going, what will happen next and what you need to do.
4. Monk
Unlike the previous professions, the monk is a full-time support character. You don't usually do direct damage to the enemy. Your job is to keep the rest of the team alive. To do so, you need awareness of the entire team status and position, as well as enemy actions. In other words, it brings together everything the previous professions taught you and adds elements of advanced strategy. Because of this, monks are most often team leaders.
What the monk will teach you:
* Awareness of all your team members' location and of the enemies.
* The importance of having all team members within reach of your spells.
* To react promptly to changes to the team's bars with heals and condition/hex removal.
* To consider the pros and cons of healing the damage after it took place vs protecting against it before it happens.
* To foresee damage coming the way of a team member and place a protection on them.
* To consider pure healing bars vs pure protection bars vs hybrid bars.
* The basics of forming teams and balacing member composition between healers, damage dealers and other support positions.
* Maintaining enchantments.
* How to split and share skills among 2 monks in areas where 2 monks are used.
* About armor-ignoring damage, and the wonderful things holy damage does to undead. How to take advantage of it by placing holy damage on your warriors.
* That smiting skills are a waste of time (but go ahead and get it out of your system).
I mentioned I'd suggest a secondary for the monk and here it is: warrior. It has the smallest amount of useful skills, so you won't be tempted (hopefully) to use them, thus focusing on monking. You will probably use certain things in Tactics, but eventually very few will actually prove useful or superior to monk skills.
5. Mesmer
The mesmer is a very special team member. She makes the enemy hurt themselves; she gives them cruel choices like doing nothing or getting punished for acting; she interrupts, disables and steals their skills. Her battle field awareness is comparable or greater than the monk's, but it is focused outward (on the enemy) rather than on the team.
What using a mesmer will teach you:
* Shutdowns (completely denying someone the ability to use their skills).
* How to tell at a glance the capabilities and nature of the enemy, by their looks, the sound of their weapons and spells, the way their spells look when they activate.
* To fine-tune your battlefield awareness to the point you can tell what's going on with everything and everybody.
* To develop your reflexes to the point you can interrupt enemy skills in split seconds.
* To put together teams and strategies based on the types of enemies you meet.
6. Necromancer
So, I've left necro for last. If you reached this point (taken 5 chars of the above professions to LA on foot while completing all quests, missions and unlocking all outposts), you are ready for the necro.
The necro is last because it can do everything the other 5 professions can, and more: point blank damage, spell damage, shutdown, healing, energy restoration, all kinds of utility positions, and that's even before we consider the unique playstyles offered by being able to raise minions.
I feel you need to master the other aspects of the game before you can fully enjoy the necro. Once you do, the necro is the profession that will allow you to unleash your creativity and your newly gained skills to the max.

The post title is misleading - your only covering prophs and not every player has prophs or all campaigns etc.Would be better if the missing campaigns ( for the begginer parts ) were added and the 4 other professions.
Agreed for the most part, although many would suggest that the other 4 professions are a little bit unusual in their roles. I wouldn't rule out using any profession as a beginner's first character. 