Plan to run three days per week until two days leading up to the race.
Run for 30 minutes two days per week. Try to space these days out.
Walk for about an hour or do a cross-training exercise, such as swimming or biking, three days per week, such as Monday, Wednesday and Friday.
Take one day per week to run a longer distance. The first week, run two miles. The second week, run three miles. On the day of the race, you will then be able to run 3.1 miles.
Pick a time of day to train for the 5K race. If the race is early in the morning, for example, try to train early. However, the most important thing is getting those runs in at some point during the day.