Finding an exercise partner to share your sweat can be a huge motivator. "You need somebody consistent -- somebody you can trust to be there," says Kerri Krasnow, a certified athletic trainer in Newport News, Va.
Look for someone on a similar exercise program. If you're both into weight training or riding stationary bikes, it shouldn't matter if you can't lift as many pounds or pedal as quickly as your partner. You can still spot and motivate each other.
A friendly competitor is good. ... Make a bet that whoever goes to the gym less often has to pay for a lunch date.
... but an aggressive one isn't. An ultra-competitive partner who pushes -- or shames -- you into a workout you're not ready for will increase your injury risk. You should be able to speak up if an exercise feels like too much. Type-A personalities also tend to do best together.
Pick someone you can look bad in front of. You're going to be sweaty, tired and likely stinky. An opposite-sex partner is fine unless you're worrying about how your hair looks.
Match schedules. Some people do better exercising in the morning and some at night, while others can only grab time on lunch breaks. Be honest upfront.
Go for a somewhat adventurous person. You don't want to jump on every exercise fad, but a buddy should be occasionally up for trying new routines.
Don't limit yourself to people you already know. Post a flier at your gym, ask the front desk staff if they know of potential partners or approach someone you regularly see there. Friends, co-workers and neighbors also may have ideas.
Look beyond the gym. Walks with neighbors or co-workers are great exercise, too.