Getting your thows right is the easiest and most noticeable thing to do. It drives me nuts to fly a plane with throws out from where I think they should be. If your plane is somewhat fast, give reduced aileron and elevator throws a shot for a few flights. I think most pilots use way too much throw on such planes -- but if you don't like it, switch back!

Also for faster planes, it's really important to have high rates for landing since your landing speed is so much different from cruising.

After that, I've found CG to be really important, particularly for landing. Nose heavy makes you sink more and makes the plane not want to flair, tail heavy makes it flighty and the stall nastier.

The rest I mostly consider fine tuning (unless it's way out of whack..). What you want to fix depends on how you fly your plane -- you might check the pattern, 3d, or pylon racing forums depending on which most closely matches your flying

Oh yeah -- on fast servos, I actually prefered the way one of my models flew with slower aileron servos; makes it feel a little smoother. This was a jet that wouldn't look right rolling abruptly, like I said it's all about what seems right to *you*