Bumping both responses, sounds like your triceps are bit underworked. If you are getting the shakes in your arms(tri's giving out) when benching don't feel bad. It's the muscles getting used to the stress load. They will go away once all of your muscle fibers in your forearms, bi's, tri's and shoulders are all working together when benching. Definatly start hitting your tri's a bit more and you'll see those shakes go away faster. Good luck bro.
p.s. doing flies first doesn't really matter much, if the tri's are weak, then they are just that - weak. No matter what exercise you start of with. But DO WARM them up first on any first set and your workout will go smoother.