Don’t start off super gung-ho and run mileage you’re unused to every single day. Utilize cross-training and yoga so you’re not suddenly running all the time—that’s a recipe for injury.
The golden rule is to not increase mileage by more than 10% per week, though if you’re just starting out and have some kind of aerobic base, you’re probably fine beginning with 20 miles per week or so.
Make sure you’ve got the basics covered, like good shoes—go to a specialty running store where someone will actually watch you run in the shoes—and recovery tools like a foam roller and yoga.