Optimal nutrition for getting in shape?

I am 6' 0" and in January I weighed 250. I decided to slim down by cutting out the midnight snack, choosing healthier items (fruits and veggies over starch and meat) and getting in shape (took up ice skating). Now I'm down to 210 and I've decided to go all the way to a "fit" body, meaning my new goal is somewhere around 180... However, I don't want to end up scrawny. I've recently started running and I soon plan to start lifting weights again in September. Now that I'm running though, it's becoming tricky because I want to burn off the fat but I want to retain as much muscle m as possible. I worry about "burning" muscle instead of fat and ending up skinny and soft, instead of the oft desired "cut" male look. So, I want to make sure I'm eating enough to keep up with my active lifestyle without hurting my body, but I don't want to eat enough to keep from losing weight. Basically, I want to eat the RIGHT stuff. How can I do that? Help? Details, I plan to do mostly moderate distance moderate pace running (3-6 miles) on day A and a brief jog and lifting on day B, alternating A and B (and resting Sunday). Lifting won't be brutal, just moderate weights and a well rounded regimen, nothing intense.