Flies should be done on chest day. They aren't a strength-building exercise, but instead are kind of a finesse/sculpting thing, so you'll want to save them at for the end of your workout and do them with higher reps and lighter weight (really squeeze them slowly). Try and do the heavy compound low-rep barbell movements first for strength, then some mid-range stuff for size, then some high-range stuff for finesse/definition.
With triceps, you basically want to make sure that you're hitting the inner, middle and outer heads.
I hit A) with a straight-bar pushdown B) with a dumbbell kickback C) with weighted dips and narrow-grip bench (though these two also hit A)
Dips are the best exercise you can do for triceps, though. Work your way up to doing them with weights hanging around your waist. This works chest and shoulders to an extent as well.
My chest day will go something like:
Strength Phase:
flat barbell bench 3x4-6
incline barbell bench 3x4-6
decline barbell bench 3x4-6
weighted dips 3x6-8
Hypertrophy/Size Phase:
Narrow-grip bench 3x8-10
Guillotine bench press 3x8-10
Straight bar pushdown 3x8-10
Burnout Phase:
Fly 2x12-15
dumbbell kickbacks 2x12-15
