Exhaust, k&ns and dynojet kit, frees up lots of ponies.
Sort chassis out so that it goes round corners better and stops quicker. Better fork springs, drop forks through yokes to quicken steering, check rearshocks and swinging arm bearings and replace as needed. Improve brakes by fitting fj 1100 or early fj1200 calipers to the front, goodrich type hoses.
nothing too expensive if items bought on ebay etc.
That should do for starters, any more and the engine needs coming out and being worked on. Then its how much you want to spend and what do you want to use it for?
No doubt everyone else has different ideas which is good as it doesn't pay to be all the same.
beeman