The best way to start out training for a marathon is to start small and work your way up. The three best main ways to train for a marathon are long distance runs, sprints and doing small local races. 

I have found that running a mile, 5 days a week, for 2 weeks is the best way to get your body back into the groove of training for any race.Once you feel comfortable going farther than a mile, start running 2 miles, then 3, then 4 and so on.

A way I have found to help me get a faster time in my mile is to do sprints. Sprints increase your speed and strength to run faster in a race. If you run the long distance and got the speed you might be ready for a 5k.

After running some local 5k's, start getting in the habit of running every week day. The best distances you could go after running a 5k is 2-3 miles everyday plus sprints for about 3-5 minutes. On the weekends (Saturday) do a long distance run, like 6-8 miles. This will help you a lot in keeping a good pace and going farther before stopping to walk during a race. When running the long distance run, make sure to go slow and go with your own pace.

When you do sprints, the best work out is only about 3-5 minutes. Most sprinters in track dont run 45 minutes a day. They stretch, run and get done. So make sure to not spend a lot of time on your speed.