Fitness Tip: Find the best fitness friend. A workout buddy is hugely helpful for keeping motivated, but it's important to find someone who will inspire—not discourage. So make a list of all your exercise-loving friends, then see who fits this criteria.

Fitness Tip: Relieve those achy muscles. After a grueling workout, there's a good chance you're going to be feeling it (we're talking sore thighs, tight calves). Relieve post-fitness aches by submerging your lower body in a cold bath (50 to 55 degrees Fahrenheit; you may have to throw some ice cubes in to get it cold enough) for 10 to 15 minutes.

Fitness Tip: Buy comfortable sneakers. You shouldn't buy kicks that hurt, bottom line! Shop in the evening—your feet swell during the day and stop in the late afternoon, so you want to shop when they're at their biggest. Also make sure the sneaks are a little roomy—enough so that you can wiggle your toes, but no more than that.

Fitness Tip: Pick your perfect playlist. Running with music is a great way to get in a groove. To pick the ultimate playlist, think about what gets you going.

Fitness Tip: When to weigh yourself. You've been following your diet for a whole week. Weigh to go! Now it's time to start tracking your progress. It's best to step on the scale in the morning before eating or drinking—and prior to plunging into your daily activities. Be sure to check your poundage at a consistent time, whether daily or weekly.

Fitness Tip: Police your portions. Does your steak take up more than half your plate? Think about cutting your serving of beef in half. That's because it's best to try and fill half your plate with veggies or a mixture of veggies and fresh fruit.

Fitness Tip: Eat this, run that. When you have a 5- or 10K (you get to eat more with a half or full marathon) on your calendar, it's important to plan out what you're going to eat the morning of the big day—something that will keep you fueled and also go down easy. While everyone is different, "We always have good luck with a high-carbohydrate breakfast such as a small bowl of oatmeal with fruit or a couple of pieces of toast with peanut butter or cream cheese,"

Fitness Tip: Turn your cheat day around. Feeling guilty about that giant ice cream sundae you enjoyed at your niece's birthday party? Don't beat yourself up! It takes a lot of calories—3,500—to gain a pound of body fat. "So really, that one off day doesn't usually result in any significant weight gain. It's about what you do the next day and the day after that's really important—so don't stay off-track. So be sure to whittle away at those extra calories over the next day or two, preferably by boosting exercise rather than eating too little.