Just go ride. I've started fresh as a lardass half a dozen times--I tend to ride for a couple of years, then take a year off, with good intentions every day. I'll gain 30 or 40 pounds, slow down, huff and puff and finally get disgusted and start riding again. When I do, I enjoy it so much I always wonder why I stopped.
Two specific suggestions: start slow, rather than beating yourself to death. Stop while you still want more, at least at first. And consider lowering your gearing. Thirty years ago i scoffed at anybody with more than about 18 teeth on their freewheels. Now I run a 46-36-24 triple with a 13-28 cassette, and I use it all.