Everything listed, plus:
-Going too heavy - going below 7-8 reps will cause probs for some people, plus for muscle development there's no compelling reason to go with lower reps.
-Wrong exercise - there are some exercises that will always be problematic, no matter what. In which case it's smart not to keep trying to "work through" the problem over and over again if it recurs, it might be that exercise. Find a good substitute; sometimes the substitute will turn out to be better. Typical problem exercises are BB bench, press behind neck, etc. but it could be anything.
-Full ROM - avoiding the top or bottom can help both to avoid injury and to maintain tension on the muscles. Good examples would be the very bottom of preacher curls, which puts inordinate stress on the tendons/ligaments without working the bis much, and squats. Bench squats can work better both in terms of gains and in terms of reduced injury potential. Hack machine squats work a little better without full ROM, IMO.
-Method of resistance: if one form causes probs, try another. Pulleys instead of free weights, machines over free weights, free weights over machines. A good example is free weight triceps extensions, which can put a lot of stress on the elbows. A pulley can give the same benefits without causing elbow stress. Same thing for cable curls, which can be easier on the joints than BB curls.
