Karen Principato is a long-time runner and self-professed cardio addict. When the Claremont, Ontario, resident first joined a gym, she stayed within her comfort zone and only attended cardio-based classes.

"I avoided Pilates and yoga at all costs. I thought they'd be too lame and boring," she says.

One day, Principato got her gym schedule mixed up; she arrived just in time for a Pilates class, not the rowing class she had expected. Rather than turn around and go home, she decided to stay.

Pilates worked Principato's body in a different way than she was used to. "It was tough!" she says. "As a newbie, I didn't see any shortcuts available to me and that was beneficial."

While she still loves cardio best, Principato now incorporates strength training, yoga and Pilates into her gym routine. Not only has broadening her approach improved her overall fitness and endurance (not to mention letting her run faster), but it has honed her mental focus, too.

"If it hadn't been for my schedule mix-up, I'd still be going to cardio-only classes and missing out on a whole other side of the fitness equation," Principato says.

Like Principato focusing too much on cardio, many of us are guilty of making mistakes when we first sign up for a gym membership. To help you make the most of your workout time, we talked to experts and got the scoop on mistakes people often make when they first join a gym—and what you should do instead.

1. Have a Plan

Walking into the gym without a plan is like heading to the grocery store without a shopping list: You end up wandering around aimlessly, not quite sure what you need and what to do. Or maybe you pick a random workout posted to YouTube or Instagram beforehand.

"You can't just show up at the gym and wing it," says trainer Ashley Borden, especially if you have a specific goal in mind like weight loss or a change in physique. Writing down and following a plan can help keep your gym time efficient too.

If you're not sure where to start, don't fret. An experienced certified personal trainer can help put together a program tailored for you, your current level of fitness and your goals.

Contact your gym and talk to a few trainers. "You want to make sure you're comfortable with them and that their approach lines up with your goals," says Kindal Boyle, NASM-certified personal trainer.

It takes time to see changes, so stick with a fitness program for six to eight weeks at least.

2. Follow a Fitness Program Tailored to Your Goals

There's no denying that we're all creatures of habit. Once you find a fitness regimen that you like, it's tempting to stay right there.

"You end up doing what you know, what you feel safe doing," says Borden.

But when you repeat the same cardio or strength training circuit over and over, your body starts to adapt. The result? You hit a plateau, halting your progress. Plus, you put yourself at risk for overuse injuries.

"When you move out of your comfort zone, you see results," Borden notes. By trying something new, you'll keep both your body and mind engaged, and your gym time won't feel boring.

So change up your routine every six to eight weeks. The gym is full of different equipment; try the rowing machine for a great aerobic session or swap your dumbbells for kettlebells or a medicine ball to challenge your muscles. If you're not sure how to use a piece of equipment, ask a staff member.

3. Try Strength Training

You like a good sweat. (We do too.) And when you want to slim down, you probably hop on the treadmill, elliptical machine or bike.

While aerobic exercise is one way to rev your metabolism, running or spinning your legs isn't the only way to burn calories. Plus, spending all your gym time on aerobic activity likely leaves less time in your schedule for strength training—which means you may be missing out on some of exercise's biggest benefits.

Strength training, everything from lifting weights to bodyweight exercises, should be a key part of everyone's fitness routine, according to Boyle. Resistance training builds muscle and bone strength, which is especially important as you get older and start to lose muscle and bone mass.

"You're not only building strength and muscle mass but you're increasing your metabolic power," Boyle says.

While both cardio and strength training burns calories while you're at the gym, your internal engine keeps humming longer after a strength training session, thanks to the so-called afterburn effect.

"You're going to get more bang for your buck," says Boyle. "You'll burn more calories up to 48 hours after you finish your workout."

So don't skip the weight room. Pencil in resistance training two to three times a week.

4. Warm Up Before Working Out

You have a limited amount of time so you want to get right to the main event. Who has time to warm up? You do if you want to avoid hurting yourself.

"Warming up is very important," says Boyle. She explains that when you jump right into a workout, whether it's cardio or strength training, your body may not be ready to take on the work. Not only will it feel like a struggle, but you may increase your risk of injury, too.

Start with a foam roller to increase blood flow and range of motion; focus on the major muscle groups like your quads, glutes, and lats. Then "do a couple of exercises that mimic the movements you're going to do," says Boyle.

5. Get a Heart Rate Monitor

If the elliptical machine says that you burned 300 calories, you burned 300 calories, right? Not quite.

"A lot of people make the mistake of thinking that the calorie burn on the cardio machine is accurate. Unless it asks you to enter your height, weight and age, or you connect your heart rate monitor to the machine, it's not accurate," says Borden.

A better way to evaluate your workout: Pay attention to your effort level. Score your effort on a scale of 0 to 10 based on your rate of perceived exertion, or RPE. If you want a more accurate calorie count, invest in a heart rate monitor, which you can connect to most cardio machines at the gym.

Remember that it takes a lot of calories burned to drop weight—3,500 to lose a pound.

6. Turn Your Phone on Airplane Mode

Watching TV or reading a book can help pass the time while you exercise. Or maybe you use your gym time to catch up on email, write your to-do list or scroll through Instagram.

While it may be tempting to multi-task at the gym, you don't want to shortchange yourself.

When you're focused on things other than your workout, your brain and body are often on autopilot and sometimes you just go through the motions. As a result, you may not be getting all the benefits of your exercise session and it may keep you from reaching your goals.

"How hard are you really working out?" asks Boyle.

Stay focused on your workout and gym time and see if your results improve. "Give yourself a set amount of time to work out, and be at the gym with a purpose," advises Borden.

7. Eat Properly

One major aspect of achieving your fitness goals is proper eating habits. While there's a lot of information about the best way to eat, hiring a nutritional coach or certified dietitian who specializes in sports and fitness nutrition can help you negotiate through all of the information out there.

One of the keys to eating properly is to determine your goals. Are you trying to lose weight? Are you trying to build more muscle mass? Are you trying to build your cardio routine and get your heart pumping more? Different fitness goals require different nutrients, including how much, how often, and when to ingest the necessary nutrients you need.

8. Get Enough Sleep

Most gym-goers understand the importance of having a fitness routine to help improve their health. Even if you work out on a regular basis, eat properly, drink plenty of water, and work with a personal fitness trainer, you'll achieve your goals quicker with restful sleep every night.

When we sleep, our muscles have time to recover after a strength training session. In addition, the body produces substances that encourage muscle and bone regeneration.

Try to get seven to eight hours of restful sleep every night so you can see better results from your workout sessions.

9. Track Your Progress

No matter what your fitness goals are, tracking your progress helps you see results and make adjustments to your routine or eating habits as needed. Let's look at a few ways that make tracking your progress easier.

• Measure your body. Take the guesswork out of your progress by taking body measurements: You can use a simple tape measure or go to a professional who can use calipers and specialized equipment to determine your numbers. In addition, take photos to visually see the changes in your body.
• Keep a workout log. Make note of how many minutes of cardio you do as well as how much time you spend on your strength training routine, stretching sessions, etc. As you add more weight, repetitions, sets, and minutes to your routines, note any improvements you see; if you're not seeing improvements, make adjustments.
• Keep a food journal. Recording everything you eat—no matter how small an amount it may seem—helps you see how many calories and macronutrients you're ingesting. Jotting down what you eat and drink helps you stay on track with your caloric intake, and it helps to ensure you're getting the right amount of essential nutrients for your health and wellness goals.
• Mix up your routine. Getting bored with a workout routine is one of the main reasons people lose interest in going to the gym. Work with a personal trainer who can help you develop new routines for each muscle group. A trainer can also help you vary your cardio program, which can include heart-pumping, high-intensity training. A trainer can help you determine what your heart rate should be for weight loss as well as for strengthening your cardio-respiratory system.

10. Do Workouts That You Enjoy

One of the keys to seeing results in your health, wellness, and fitness goals is consistency. It's easier to stay consistent when you choose exercises that you enjoy.

Don't like running? Go to a dance class for your cardio. Don't like using machines at the gym for your strength training routine? Use bodyweight exercises in the comfort of your home instead.

Whether you like yoga or are a hardcore gym rat, find exercises that resonate with your lifestyle, are safe for your fitness level, and that you want to do on a consistent basis.