Couple of things nobody mentioned yet.
Learn hiding spots/sticky trap spots. check them.
Use you
shotgun to clear stickies. Your medic won't like stickies suddenly rolling towards them from a rocket blast.
Unless you're deliberately building uber with a scout, build uber. But watch you ammo and snag ammo packs regularly.
also, bears repeating
Dont think twice.
Hesitation gets your medic killed.