It's the same old story. You sign up for a gym membership, and weeks later you find yourself short on time and long on reasons to avoid the health club. Or, that home-gym purchase turns into a really expensive place to hang clothes in the corner of your bedroom.

We could point the finger in a few directions, but it's simple: instant gratification. We download songs and movies within moments, take pictures, e-mail and text from our phones and shop with the click of a mouse. We get what we want and fast.

But not with fitness. Getting the body you desire takes time. So, to keep you on track, I propose five tips for sticking with it:

1. Write yourself a note that says, "Stick with it—it will work." If it sounds like a Chinese proverb, that's because the sentiment is timeless and true. With daily reminders of what you're working toward, you become your own motivational guru.
2. I wish I had a penny for each time I'm asked, "Can I look like Jessica Simpson?" Keep your goals realistic and simple and forget the number on the scale or fitting some mold. Have a goal chart. This isn't just about losing weight—it's about creating healthy habits, like getting workouts in and eating five small meals a day. Each time you meet a goal, celebrate it.
3. A scientific plan is key. Make sure it combines cardio and strength training and a schedule for your workout. Structure the specific number of reps, sets and resistance for each exercise—the structure and consistency bring results. But don't mistake science and structure for stagnation. Not only do our brains get bored with doing the same things over and over, so do our bodies. If you want to keep changing your body, your program must keep changing, too.
4. How do we know where we're going if we don't know where we've been? A simple log should list when you work out and the exercises, sets, reps and resistance you do. If you fall off the wagon (hey, we've all done it), just jump right back on where you dropped off.
5. It helps to have folks cheering you on when you succeed and dusting you off when you've failed. They provide insight and motivation and keep you honest. So call a friend and get started down the path of healthy living.
   

Harley Pasternak, the man famous for getting Halle Berry into her catsuit, got his start training Jim Caviezel for Angel Eyes. His roster now includes everyone from Robert Downey Jr. to Alicia Keys and Kanye West. This L.A.-based trainer-to-the-stars has two fitness and nutrition books under his belt (5-Factor Fitness and The 5-Factor Diet) and has appeared on The Oprah Winfrey Show, The Today Show, E! and VH1.