Just reach l lvl 51 and need advise on the first aa I need and about posions since I have not looked into them or used them
Bite of the Shissar <insert roman numeral here> are available for sale on the poison vendors in PoK in the building between guild lobby and bazaar entrances. At low levels they're very powerful.
Yes, make sure you are always using a DPS poison (Bite of the Shissar) and if you can try to keep a utility posion up. The DPS from the poisons are a huge boost.
I personally feel Shroud of Stealth is the first AA to go for. Following that I would go combat fury/ingenuity...the critical procs on the poisons are rediculous.