It depends on how far before conception you are talking about, but I can highly recommend a series of colonic hydrotherapy for a great detox- a series of 3-5 over the course of a few weeks, while drinking a ton of water and super green food smoothies and stuff (basically eating well and being very hydrated helps the colonics be effective). If you haven't had it done before, it's not anywhere near as bad as you are probably thinking- I didn't find it unpleasant at all.
You might find some good suggestions in the Health forums.
I focused on vitamins/supplements, increasing my water intake, working out regularly, and trying to cut out junk. I did a colonic hydrotherapy series about a year ago, and although I'd like to do another, I don't think it's recommended if you are pregnant or about to be really soon.