It is always best to perform exercises which are most complex first. Fatiguing your muscles, nervous system and/or metabolic pathways prior to performing complex movements can be detrimental to both performance and safety.
Complex, or "compound" exercises can be defined as those which involve use of multiple joints, muscle groups and/or movement patterns. Squats are good examples of a compound/complex movements.
For example, on our Press/PushPress/Jerk workout - get a good warm-up (row) and perform several lighter sets of jerks before piling the weight on. Next go to the pushpress exercise. Then, form up on the OH presses. Rest as much as you need between exercises and sets. You should be fully recharged before attempting another set. You only get 3 sets per exercise so each one must count to gain max benefit.