If you haven't really worked out since your gym class days, then a St. Patrick's Day marathon is probably not in the cards for you. But a 5k by then is likely doable, and having a race or event in mind can help keep you motivated.

If you're not into racing, then set another goal that works with your fitness level. Maybe you want to move up to the advanced yoga class by spring or even just make the most of your newly acquired gym membership. Whatever it is, make your goal something that gets you excited to work out, but isn't so ambitious that you're setting yourself up for failure. "Remember to push yourself, but not to the point of feeling ill or injury," says Angeles Burke, Celsius.com Fitness Ambassador. "In order to see the changes you want, you must challenge yourself in a way you never have before."

Lack of time is a common excuse for skipping your workout, so you've got to make exercise a priority in your schedule, says Janette Janero, a personal trainer and group fitness director at Florida International University and The University of Miami Wellness Center. "I recommend setting aside one hour for walking and 15-second stretch holds for each major muscle group at the end of the workout," she says. "Setting aside this time every day will help you get used to incorporating exercise into your schedule, even if it is not at a high intensity just yet. Routine helps condition muscles to be prepared to handle cardio activity."

Stretching can easily get overlooked when you first start working out, but it's so crucial. "Better flexibility leads to fewer injuries, which allows you to stay on routine and continue living an active lifestyle," Janero says.

One caveat, you don't want to stretch at the very beginning of your workout. "If you stretch a muscle that is 'cold' you are more prone to injury," Burke says. So do your stretching after at least a few minutes of walking or jogging.

Below, Burke outlines several key stretches:

•Toe Reach: While standing with feet together, keep back flat and shoulders back as you reach for your toes. Only drop down as far as you can until you feel light tension in your hamstrings (back of thigh). Going too far may result in injury. Slowly release and come back to a standing upright position. And repeat 3 times and hold for 10 seconds each. This stretches hamstrings, gluteus, and lower back.

•Flamingo Hold: Hold on to something stable for balance. Place all weight on left foot and bring heel of right foot to your glute while standing as tall as possible. Repeat on opposite leg. Hold for 12 seconds and repeat 2 times per side. This stretches your quadriceps and hip flexors.

•Body Huggers: Standing tall, extend arms fully out to side and push them back while taking a deep breath in. exhale and wrap arms around your torso (as if you were hugging yourself). Repeat 15 times and hold in open position for 3 seconds. This stretches your chest while warming up back and shoulder muscles.

Janero has a simple move that even the least fit of us can try to get started. "Fitness beginners can start with something as simple as sitting at the edge of a chair with feet placed shoulder width apart and knees at a 90-degree angle," she says. "Once in position, stand up and squat back, repeat 15 to 20 times slowly. This form is the foundation for the perfect squat."

Janero recommends doing 2 to 3 sets of squats every other day to get your lower half ready for more intense exercise. She also recommends starting with some basic cardio, either walking or light jogging. "If you don't run a 5k the first month or two don't worry," she says. "The important part is just being active. You WILL get there."

You're walking, you're stretching, you're starting to get in the groove, so now Burke has a simple routine to step things up a bit. "Doing at-home circuit training is a good way to kick things off," she says. "This way, you do not need to learn how to use all the fancy gym equipment right off the bat and you can push yourself to your limit." Here's what to do:

Circuit: 5 rounds as fast as possible

15 jumping jacks
10 walking lunges
10 mountain climbers
5 pushups

"This is a total body workout that will get your heart rate up as well as target major muscle groups," Burke says. "As it becomes less challenging, add more repetitions or a new move. Always switch it up and look for a new challenge to keep your body guessing."