My advice for any new assassin is always this. Run either full darkness
or a hybrid
until you start getting some decent gear and start pumping out the damage. This is for 50 PvP, lowbie PvP you can run whatever but trust me run some variation of darkness when you reach 50 you will have a more enjoyable experience.
^ This is good advice for you OP.
I ran a classic hybrid, like that cycao linked, for a while and found it to be really good while leveling. Sins rely on clever tactics and timing a bit more than some other classes, so there's a learning curve. Once you get them down I'm sure you'll love it.