You're paying for it, so you deserve to get the most out of your gym membership, but if you're making any of these common workout mistakes, you're not getting the most bang for your buck. Follow these expert tips and you're sure to see a difference in your workout.

1. You're not using the heavy weights: It can be intimidating to venture out onto the weight room floor, especially when it's full of bodybuilding types throwing weights around. But you aren't doing yourself any favors by staying in the corner with those little pink dumbbells! "You have two types of muscle fibers: slow and fast. If you don't use heavier weights, you neglect an entire set of muscle fibers, namely the fast fibers, which are important for moving quickly, lifting weighty objects (your heavy purse, grocery bag, suitcase), and for spine and hip stability," says Michele Olson, Ph.D., professor of exercise science at Auburn University Montgomery and creator of the Perfect Legs, Glutes & Abs DVD.

And if you're worried that you'll bulk up, don't be. "Women cannot add much size to their muscles to begin with since we have low concentrations of the male hormone testosterone, which is necessary to enlarge muscle to any noticeable degree," Olson says.

2. You don't have a plan: Do you want to lose 10 pounds, run a 5K, or become more flexible? "There are special workout plans for each of the above, and they are not interchangeable-there is no "one exercise-fits-all" program, " Olson says. "If you do not have a plan to address your greatest fitness needs and desires, you can stall results and actually create changes you do not need or that might not even be appropriate for you."

Your primary objective (weight loss, endurance, strength) should influence the volume (amount you do), intensity (how light or hard/heavy) and the mode (cardio, resistance exercises, stretching programs) of every workout, which is why Olson says it's so important to take the time to meet with a qualified trainer at your gym for an assessment and to help create your goal-specific program.

3. You don't "pound" enough to protect your bones: You already know that it's important to do weight-bearing exercise to help protect your bones, but you may not realize just how much loading you need to do in order to reap the bone density benefits. "While treadmill walking is sufficient to keep the spinal bones strong, your hip bones need more loading," Olson says. "To  do this, think "steep," or "stomp." If you want to stick to walking, increase the incline on the treadmill to seven percent for 3 minutes, followed by 5 minutes on level ground, alternating five times during a 40-minute workout. Other options: Take a step class, use that machine with the revolving stairs, or walk the stairs in your gym. This extra impact is not too heavy but at a level that is much more effective at getting your hip bones to take up more calcium and become more dense.

4. You don't push yourself hard enough: You may have just spent 2 hours at the gym, but how much of that time were you intensely exercising? Yes, fitness should be fun, but if your set routine involves reading a magazine on a card machine followed by the same weight machine circuit, chances are you aren't seeing the results you want. "In the beginning exercise can feel unruly and even excruciating-which is clearly not fun-but once your body learns how to do various exercise movements and your strength and stamina improve, it's time to upgrade your program." Olson says. "Time and again research has shown that increasing to more vigorous levels of activity bring about greater health benefits and noticeably improved fitness and appearance." And you don't have to spend more time at the gym. In fact, if you focus on the quality of your workout, you may actually spend less time there. "This is why interval training has become so popular," Olsen says. Experts recommend a range of intensity levels, but many interval workouts go up to 85 percent or your max heart rate. "If you can learn to push yourself appropriately, you can also land the benefit of a higher metabolism following exercise -that means you are rewarded for your extra effort following exercise with an extra energy burn!"

5. You don't take advantage of experts: "If your club has trainers, movement specialists, physical therapists, nutritionists, or registered dietitians, use them!" Olson says. "They are skilled to determine some needs you may have that are not obvious but could prevent you from making progress or possibly be causing you injury."

This is especially important if your goal is weight loss. If you're trying to lose weight, what you eat is incredibly important, especially if you're regularly exercising.

"A trained expert can speed up your progress and results as well as prevent you from burning out, under-eating, or over-doing," Olsen says.