You wouldn't want to work a smaller muscle first that assists a larger muscle later, as in, working on triceps before chest or shoulders or biceps before back. The smaller arm muscles are already a weak link in the chain, and training them first will only sabotage the effectiveness of your workout.
Is it better to do all tricep workouts before switching to biceps or should you rotate. So after you have done a good deal of biceps first, triceps later, switch.. Train each part until you cannot perform a full rep, then switch it over, back and forth.