In general, you are considered a heavier runner if you are a man and weigh more than 185 pound and over 150 pounds for a woman.
It is important to know your Body Mass Index (BMI). However, that does not show the whole picture for those with larger frames or those who have large muscle mass. Do not worry if you do not look like a "runner." When you line up for a race look around and see all the different body types.
Here are some guidelines for heavier runners:
1. Go to a specialty running store to have your foot and gait evaluated: larger runners often have flat feet and a tendency to overpronate, look for a durable, motion control shoe that has plenty of support and cushioning, in general, do not buy the lightest shoe out there.
2. You may have to replace your shoes more often (each 300-400 miles as opposed to 500 for lighter runners).
3. Realize that you may be more prone to injury due to the increased force created with your foot strike.
4. Alternate running days with lower impact cross training.
5. If you are new to running, start slow and consider a run / walk program, slow and steady will lead to success.
6. Learn and practice good running form, you want to be propelling forward, not rising up and down.
7. Listen to your body, slow down if you experience injury or constant pain.
8. Do not be discouraged if you do not lose weight right away, building muscle will cause the numbers on the scale not to go down right away, but remember that muscle burns more calories than fat.
9. Make sure to hydrate before, during, and after a run.
10. Practice good nutrition: you may be hungrier after starting to run, but you do not needlessly need to eat more, quality over quantity.
11. Purchase some running clothes that you look good in: it will motivate you to get out more often, if you're embarrassed by how you look you might not do as much as you could.