I would just try to be more healthy in general, which is always good, not only when ttc. Also I think it helps to develop good habits for when you're pregnant. So that would mean less caffeine (you could switch to decaf) and less alcohol. You could also cut down on sugar and eat more wholemeal stuff, vegetables and fruit and switch ready meals for home cooked food. But it's important you're not forcing yourself in anything too strict, as it's important you're feeling good and happy as well. So in my case I still enjoy sweet things, as I don't want to lose weight either, but just less than before by eating healthier snacks.
Furthermore, take prenatal vitamins, they have everything in them you'll need. And exercise, although don't start running marathons or anything.