If playing DRK, don't forget about your Binds/Sleeps/Stuns! Magic is a big deal in Ballista and it's really not hard to land.
Poisonga strips shadows, just don't try to sleep after!
If you're gonna do something "obvious" like Souleater (since it signals you're about to WS), make sure the enemy can't Third Eye/outrun it
Don't neglect your Drains!
Your role as a DRK is to perform basic crowd control functions while having the ability to run in and oneshot (or almost oneshot) -most- jobs. You can cripple magic casting jobs with your Guillotine which is VERY handy with BLUs (don't approach one without)! If you end up in a lengthy 1v1 with a BLU, just sleep > aspir > sleep > aspir until the MP is all gone, though this rarely happens.
As for idle gear, I wouldn't put too much emphasis on Haste. AF(+1) head is good for Dark Magic/Souleater, Parade Gorget is unlikely to help much since you should be using Souleater a lot so don't worry about it too much... Ethereal Earring is VERY sexy indeed, Chaos+1 are a fine pair of hands, and use Crimson Cuisses if you have them. It's worth considering using Jelly/Patronus Rings too perhaps... you shouldn't have accuracy problems on anything that's not trying to evade.
Also be careful of using a Haubergeon-line armour piece in 60cap... SAM/RNG can really fuck your world up when it doesn't miss those Sidewinders.