Where to start-
For beginning players, usually others will say Prophecies. It is a long game compared to the others but good to help you pick up the ropes. If you have Eye of the North, play till you reach Lion's Arch and go do the simple quest that will bring you to Boreal Station in the North and get a few Heroes to bring back with you to help you along the rest of Tyria's missions. The heroes there are at level 20. No need to level them.
Factions is a really fast game. You may be level 20 by the time you get out of tutorial island. One thing good about this game is the fast leveling and the skills. Once you have got out of tutorial island, you can go straight to the Eye of the North to get the Heroes to bring back.
Nightfall, to me, is extremely fun but not as easy as the rest. But it has the most number of Heroes with a spread of professions to acquire. But I think Nightfall is better when you know what you are doing.
If I were giving advice, I would say try Factions first but that is just me. But what I did was to play all three games here and there until I am happy.
Where to go-
Guru home page has a list of all missions from all lands. Wiki has everything. Just type in the name of what you are looking for and all information on it come out. A comprehensive list of all missions and quests with maps are also there for you. I use it to look for skill trainers, storyline of Npcs, skills, missions, maps, quests... everything. Lots of players also put in how they beat missions on Youtube. I like LiquidSolenoid's gameplay because he takes you through fast. It can get boring for some people, watching the game play but it helps me get ready for what to expect.
http://www.youtube.com/user/LiquidSolenoid
what to do
Again, wiki and guru can help you greatly on that.
how to go about picking out skills
Skills can be bought from skills trainers or picked up as you play the quests. unlocking a skill will unlock for all Heroes of that class. Each campaign has their own specific skills so remember to check with trainers when you see one in a town post. Elite skills are captured but to get that skills you will need to fulfill a quest first.
how to make money while playing
Go out there and kill something. Farming builds are all over as well Just hunt for them.
I don't usually farm except keeping a character in pre-searing for dye farming which I don't usually use except on very boring days at work. I get lots just playing through Fractions and Nightfall. Prophecies cash drops are slower so you get the bigger drops only at the end of the game.
I'm trying to decide between a Warrior and a Necromancer (both look like a lot of fun!
) so I can start in any campaign.
Just start as many character as you want and see what suits you best. You may surprise yourself.