Just start riding, monitor your weight, and eat the best diet you possibly can. Experience will tell you what you need to eat during rides (my advice is to have plenty available -- I need more than I would have thought possible, and it feels awful to not eat enough).

Especially in winter, I burn so many calories cycling that I eat all the time. At first, I fell into some bad habits -- filling up on cheese and crackers, for example. I improved my planning/shopping skills, and did much better during my second winter of cycling.

The TE food/nutrition threads are a great resource for ideas and inspiration. One example is this recipe for Almond Butter Brownies -- yummy and nutritious, and I'm just about to make some with pumpkin.