If you're having trouble getting your combo off, you could try using a Warrior secondary and running with [skill=text]Flurry[/skill]. IAS is your friend.
You getting killed as soon as you're targeted? Well... there's not too much that can be done for that. You have to keep in mind that Assassins don't have strong armor (max 70 AL) and are not meant to stand up to focused fire for any significant length of time. A/Mo builds do exist which let you tank, but they're pretty specialized. They'll let you take advantage of Golden Phoenix Strike, but there isn't much room in those builds for hexes, which knocks out the Black Lotus/Spider Strike off-hands.
If you're hexing your opponents or using an enchantment on yourself, you have [skill=text]Black Lotus Strike[/skill], [skill=text]Black Spider Strike[/skill], and [skill=text]Golden Phoenix Strike[/skill] as off-hands available to you that ignore the use of lead attacks. [skill=text]Assassin's Promise[/skill] is a commonly used hex. Go for that if you think you can knock off your opponent in time. Another cheap hex is [skill=text]Parasitic Bond[/skill]; if you have concerns about being able to kill your opponent in time, or want to confuse opposing healers, I think this is the hex of choice. Eminently spammable, gives you a little health loving when its time is done (or your opponent dies)... I like it.
I can't claim to be awesome, but these are some fairly standard suggestions that should help you out. As always, check out
the builds at GuildWiki to see if there's something you want to emulate, or would like to use as a base to develop your own skillbar.
Good luck!
