As others have said, mix it up with walking. I started by running for one minute and walking for two minutes and that progressed to running for two minutes to walking for one minute.
And after nearly a year I've built that up 'n' up and tomorrow I'm doing an 11 mile easy, bringing my weekly total to just over 30 miles.
Keep a diary, right from the beginning; log the time you train for; all the details; and it's great to reflect upon a few months down the line; you can really see the progress you're making.
And enjoy it; I have to remind myself it's not about times and personal bests; but about just enjoying the freedom of movement and being outdoors (even if it is raining).