Unless you have limitless time at your disposal, not to mention the discipline of an Olympic athlete, your workouts probably don't span longer than an hour, hour and a half -- tops. More likely than not, they probably even take less time than that -- which is perfectly OK. When it comes to getting into better physical shape, quality should always win out over quantity, which is why it's imperative to maximize your time in the gym.

One way to do this is to avoid spending time on detailing exercises. If your goal is to drop some pounds, tone up your muscles and improve your overall health, doing a bunch of bicep curls and leg extensions just ain't gonna' cut it. These exercises are used by seasoned exercisers to fine-tune their physique; they should not be used by beginner or intermediate lifters who are in the early stages of rebuilding their body. Remember, with only an hour or less a day to fit in your workout, you have to make every single minute count. This means leaving exercises such as pec deck flys and other isolation movements to the gym vets, while you instead turn your attention to calorie-burning compound exercises (i.e. squats, deadlifts, bench press, pull-ups, push-ups, etc.).
Bear in mind that every time you press a weight, you use your triceps; every time you pull a weight, you use your biceps. Similarly, you work your quads, glutes and hamstrings whey you perform most leg pressing exercises. Therefore, it's not really necessary to spend time performing dozens of sets of bicep curls or tricep extensions, just as doing sets of lying hamstring curls won't make or break your workout. Don't fall into the trap so many lifters fall into: don't squander your time at the gym with isolation movements -- not at this stage of the game, anyway. Once you have built a nice, solid foundation, then you can go back and start working on all the trimmings.