i ran alot in the past, quit and got fat, lost weight and now i run again!
to answer your question, it's going to be a matter of increasing your millage and days running, plus listening to your body.
take your resting pulse rate every morning before getting out of bed. write that number down. if you notice your pulse rate increasing by about 10 beats, take the next day or so off (until the rate retuns to normal). an increase in heart rate indicates overtraining and will lead to injury, and also slow your progress.
i usually run 3 days on 1 day off. i run one long run per week.
i doubt if i'll ever race again, but i enjoy running.
BTW-the link brother Johnson posted is a great site.