Well... I guess if you are talking about basics... and its no buying of new guitar, just upgrading...
I'd say make sure your guitar stays in tune first. Like if you got a crap Floyd Rose imitation that just doesn't keep its tuning, you could get all the best gear in the world but then, you'll be out of tune and sound absolutely horrible. So yeah, if you are going for upgrades only, I'll say make sure the guitar stays in tune, be it the tuners or bridge.
Then there's always pups if you find you don't have that much cash for a brand new Floyd Rose or something...
For me, I always go for the basics... if what you have in your hands sounds good and feels good, chances are you'll sound good and play better.