Whether you're prepping for your first 5K or a marathon, these tips and plans will help you reach your goal.

1. Build slowly
When you prepare for a marathon, it's mainly about building up mileage to a point where your body—and mind—can handle 26 miles (the mileage in a marathon). After a couple of months of increasing your mileage, runner and trainer-to-the-stars Wes Okerson recommends doing two short runs (4 to 5 miles), two intermediate runs (6 to 8 miles) and one long run (10 to eventually 18 miles) per week. Completing 40 to 50 miles a week puts you on track.
2. Map out a schedule
Pick a day of the week when you know you're not busy and make that the day you'll do your long run. Make an effort to fit in short or intermediate runs before or after work, but be sure to space them out so you're not running late in the evening and then early the next morning. You want to give your body about 24 hours to recover between sessions.
3. Avoid common mistakes
Common mistakes people make in training include not running far enough. If you've only done 12 or 14 miles, you're going to have trouble completing 26. On the other end of the spectrum, there are people who are doing way too much. They're abusing their bodies and getting overuse injuries. You don't have to do an excessive amount of mileage. As long as you have a plan in place and are running four to six days a week and resting at least once a week, you should be fine.
4. Cross-train
This is vital because it enables you to give your running muscles a rest and use your body in a different way. With running, you're only moving in one plane with one motion and it can be very stressful on the joints. It doesn't matter what activity you do to cross-train as long as you're keeping your heart rate at 60 to 70 percent of your maximum.