For many runners, the desire to do a marathon is about personal challenge. You might want to test your limits or prove that you can go the distance. Perhaps a friend has talked you into it. Maybe you'd like to lose weight, get healthier or raise awareness for a charity.
Whatever your reason, hold on to it and remind yourself of it often during the months that lie ahead. When your legs are tired or the weather is nasty, maintaining your motivation will help you get out the door.
For an overview on how to get started in the sport—including shoe selection, stretching techniques and proper mechanics—see the REI Expert Advice article, Running Basics.
Be aware of your limits. The 26.2 miles in a marathon put you at a significantly higher risk for injury than your daily neighborhood jogs. Consult with your physician before embarking on any training program.
Start early: Conventional wisdom recommends that aspiring marathoners run consistent base mileage for at least a year before embarking on a marathon training program.
One of the most common causes of injury is building weekly mileage too soon, too fast—so don't underestimate the importance of consistently running at least 20–30 miles a week regularly before committing to training for a marathon.