Accuracy and efficiency will be improved by a consistent air flow...so, replace teh front reg (teh one you hold) with a CP Reg or better, these look good, are available in several colours and most of all, work very well, they cost around £40 new, but can be found Secondhand...come to think of it, I have a Dye Hyper 2 reg in Black...very good reg, off of my DM4 you can have for £30 if you like.
Make sure your main tank reg is as consistent as possible too.
Fitting a QEV or Quick Exhaust Valve, will enavble faster cycling (when upgrade boards are available), better efficiency as well, caused by lower Dwell times.
A good barrel set is a must for any serious baller...or one or two barrels that suit teh size of paint you mostly use...paint to barrel match is the last stage of accuracy (apart from actually being able to aim the gun!)
Get a decent roller trigger as well, as the standard ones can break and look ****e...the roller trigger will also help to shoot faster in semi mode...
There are also some Bolt kits available, one from Orange at least that I know of, tho I dont have any experience of what they claim to do.
You might not, buy an Angel...