I am darkness PvP in DPS gear. My layout is as follows.
I try to somewhat group my buttons.
1-5 wither | shock | thrash | overload | whirlwind
ctrl 1-5 saber strike | force lightning | jolt | electrocute | assassinate
alt 1-5 discharge | spike | force speed | force pull | mind tap
mouse | scroll up = unbreakable will | scroll down = force shroud | mouse 3 = recklessness | mouse 4 = stealth | mouse 5 = deflection
R = mind control
T = mass mind control
Y = trinket
F = force slow
G = guard
H = huttball
V = overcharge saber
If stealthed I open with spike - wither - shock - Force lightning at 2 stacks (if I need a heal I will thrash and then I trinket and pop recklessness hit them with a shock Force lightning), assassinate always gains priority. When not stealthed I usually save spike for interrupt. My rotation changes constantly though. If it's a heal I will not spam abilities so I can have stuns and interrupts ready. If I am against a noob I will just wither, shock, force lightning them over and over while throwing in stuns and interrupts and switching to the wither, shock, thrash, shock rotation for the heal force lightning when I need it. When I'm waiting on shock or wither CD and I'm around multiple enemies I throw in discharges. Oh, and always keep mind control and mass mind control up as well as force slow when needed.
Also, I have no problem memorizing every ability I listed, and I smoke a lot of dro. Not sure what these guys are talking about you can only have 10 memorized. Set them to ctrl and alt 1-5 and they're very easy, but I've been playing with that setup for at least 6 years