There are some simple, generally accepted rules of how to properly sequence exercises in resistance training workouts. While, no doubt, many of you will already know these things, many may not. And because it is such a crucial part of routine design, no series of this sort would be complete without addressing exercise sequence.
Unless under special circumstances, the free-weight compound exercises should always be placed near the beginning of the session (usually at the very beginning). This is partly because they are the most demanding exercises in the routine (both physically and mentally) and partly because they involve many muscles - all of which you want 'fresh' for the big effort that these exercises require. If these exercises were placed at the end of the routine you wouldn't likely have the mental or physical energy left to do them justice, and would, therefore, short-change yourself on the most productive exercises in your routine. By the same argument, particularly demanding compound exercises should be placed before less demanding ones (e.g. Squats before Bench Presses).
The compound exercises also involve many other muscles in addition to the prime movers, including smaller stabilizing muscles (see the article entitled Making A Strength/Size Routine Part I: Exercise Selection), which must be rested if performance of the exercises is to be optimal. If the isolation exercises were done before the free-weight compound exercises, muscles that are needed for performance of the compound movements may have already been fatigued (depending on the isolation exercises performed, of course). This is an especially detrimental situation if the muscles fatigued are not the prime movers of the compound exercises, but are stabilizers. Even if the muscles fatigued were the prime movers of the compound exercises (a deliberate technique used by some, known as "pre-exhaustion") this is not the proper route for drug-free, genetically average weight trainers, most of the time. Pre-exhaustion limits the amount of weight which can be used in the all-important compound exercises and, therefore, also limits anabolic hormone secretion in response to those exercises as well as the absolute tension that the targeted muscle fibers are capable of developing.
Exceptions to this rule would be special circumstances such as working around an injured bodypart, or the utilizing of pre-exhaustion based cycles for the sake of variety (i.e. in response to both physical and mental staleness). In those, relatively infrequent circumstances, the free-weight compound exercises are performed after isolation exercises in the training session. If a trainee has difficulty "feeling" the target muscle work during a compound exercise for that muscle group, then I sometimes have them perform a 'peak contraction' isolation exercise for that muscle group before the compound exercise. This is done as a special measure to establish a stronger mind-muscle connection to that muscle group during the compound exercise. Once a strong mind-muscle connection is established I no longer have the trainee perform the peak contraction exercise.
In addition, how the compound exercises relate to each other must also be considered. Doing a certain compound exercise may hinder performance in a subsequent compound exercise, but the two may be able to be reversed without adverse effects. For example, Deadlifting before Squatting would likely severely limit Squat performance because of lower back fatigue, but Squatting before Deadlifting may not have that much of a detrimental effect on Deadlifting performance.
A general order sequence of compound exercises would be as follows (keep in mind that this is just a general list and is not necessarily meant to be completed as a single workout):
A few words of explanation are in order: The Olympic-style lifts are performed first because they are high skill movements and are susceptible to technique breakdown if any of the numerous involved muscles are fatigued. Some people may also choose to do Bench Presses before Deadlifts because Deadlifts can limit Bench Press performance by fatiguing the shoulder girdle. There are, no doubt, a few other questions that could arise regarding the above sequence but, generally (barring any special circumstances), it is a good order to heed. Of course, it is unlikely that anybody would want to perform all of these exercises on the same day - but, depending on personal factors, some people may.
Isolation exercises also have to be considered with regard to muscular fatigue. As eluded to above, it wouldn't be wise to do Back Extensions before Squats (they would fatigue the lower back) or to do rotator cuff exercises before Bench Presses (it would limit Bench Press performance because of shoulder fatigue and, therefore, instability). The very general guideline would be to place isolation exercises that strengthen the stabilizer muscles of the body towards the end of the workout, after all the compound movements have been done. It wouldn't matter a great deal, however, if you did Back Extensions (isolation for the lower back) before Bench Presses. These two exercises do not, generally, conflict with each other - unless, you are performing power-style Bench Presses with an exaggerated arch.
Many weight trainers like to complete all the exercises aimed at stressing a particular bodypart consecutively. Using the above example of Back Extensions, this means that if Squats and Back Extensions are to be performed in the same workout, the Back Extensions would be performed immediately following the Squats and not at the end of the workout (Squats would likely be placed at the beginning of the workout). As long as no lower back intensive exercises are to follow (e.g. Bent-Over Rows) then there is nothing wrong with that approach.
Below are some examples of possible workout exercise sequences utilizing split routines.
Below is an example of a full-body workout exercise sequence.
Alternately, and apparently "bending" a general rule outlined above, Squats are sometimes performed later in the routine (after other compound exercises that don't overly fatigue the muscles involved in Squating). This is done by some trainees because Squats can be very "draining" and leave the lifter too tired to train the other compound exercises effectively afterwards. Below is an example of such a full-body workout exercise sequence.
NOTE: As you can see, these routines don't contain many isolation exercises. If you are a drug-free, genetically average weight trainer who is interested in results you will find that you simply cannot tolerate many of them. Other articles on this website will outline how, and when, to include more isolation exercises in your routines.
The above are only a few of many possible exercise sequences and choices, but I hope that they, along with the rest of this article, have given you an idea of how to structure your routines in the most productive manner.