What's the next step to upgrading my currently stock AEG?

[MagpieTactical]

Echo most of the advice in here. 

On all of my guns, bar my sniper rifle, all I have done is changed barrel to a ZCI, and fitted a decent hop rubber (prommy purple, G&G green, or the light blue G&G in the rotary hops) and used some heavier bbs. Rarely out ranged at my local site, and requires very little time/difficulty to do