should you do chest press or pec flys first when training?

Answer 1

Flys don't really do that much good for you. You are better off doing dumbbell chest presses.

Always start with the exercise that puts the most weight in the most unbalanced position. The minor muscles that balance the weights are the first to go. So many will start with the dumbbell chest press, then do the barbell chest press and then finish with the machine chest press. There is no balance needed on the machine chest press so you are only working your core chest muscles. But you need to develop the minor muscles that help you balance the weight, which is why you start with the dumbbells (since they can independantly move in any direction).

Answer 2

Do the hardest first. PREss first, incrementing the weight , then do flys, with lighter weights ,

Answer 3

for the most part, you want to do your compound movements (i.e. presses) before your isolation movements (i.e. flyes). that said, you can also use pre-exhaustion to your advantage sometimes by doing the opposite. it really just depends on what your goals are, etc.