Enchants:
Cloak - change Agility to Crit, it's a slight DPS increase (according to EJ)
Bracers - Enchant Agility over haste, haste is assassination's third stat to prioritize
Gloves - Mastery over Haste
Stats:
Hit to
1127 (17%) which is the spell hit cap. Poisons are considered spells, so at 17%, as long as your attack lands, poisons will be applied
Mastery - No cap, stack as much as you can
Haste - No cap, stack as much as you can without taking away from either hit or mastery
Expertise/Crit - Neither are a good stat for Assassination, so they should be removed from gear at all times
Gems:
Red - Delicate Inferno Ruby
Yellow - Adept Ember Topaz (mastery + agi)
Blue - Glinting Demonseye
I see you're a JC, so use your JC gems for 3 of the reds (obviously)
So, there are a list of changes that need to be made. You can use WoWReforge.com for reforging (you have Riplimb's Lost Collar which has exp and crit on it, yet it's not reforged.... So, you need to run WoWReforge to find all the reforging you need to do. My character has a ton of reforging going on, I only see two on yours, so I'm sure you're not reforged correctly. Not an insult, you asked for help...).
Go to
http://elitistjerks.com/f78/t110134-..._06_28_2011_a/ for more help. It has all the stat weights, etc that you'll need to use on WoWReforge as well as gemming, enchanting, and rotation help