If you don't know your way around a weight room, heading to the gym can be intimidating -- and even dangerous . But paying attention to a few simple rules of proper technique can make you slimmer, stronger and healthier all over.

We spent an afternoon at Equinox with trainer and manager Rebecca Woll, learning the ins and outs of some of the most popular strength-training machines.

In the coming weeks, we'll be sharing Woll's thoughts on the biggest mistakes we all make while building muscle, plus her tips and tricks for better form. This week, we're perfecting the seated leg press .

The Faux Pas: The most common mistakes, says Woll, are allowing your head to pop off the bench, with your chin tucked, or allowing your lower back to do the same. "We all have lower back issues, so we never want to 'load' a lower back," says Woll, which can lead to injury and will take the emphasis off of those legs. Others use this machine too fast, allowing momentum to do more of the work than those muscles!

The Fix: First, make sure your knees are bent at about 90 degrees, and move your feet up so that your shins are parallel to the floor, she says. If it helps you to visualize the correct posture, "it emulates a squat," says Woll. Then remember that the back of your head and from the middle of your spine all the way down to your hips should be flush against the bench, she says. Press down through your heels and feet and into your big toe until your legs are extended all the way, keeping the knees soft rather than locked, then lower back down. Remember to press slowly enough that you feel your muscles firing, she says.

Tell us how it goes in the comments below, and be sure to check back over the following weeks to fix your form on the row machine, the lat pulldown and more.

Check out more in our Fix Your Form series below:

Photos by Damon Dahlen, AOL

For more on fitness and exercise, click here .