I keep up with my shots and take a glance at the CDC's website before I go to a developing country. I'd like to avoid hepatitis A, thankyouverymuch.

Other than that, I think basic precautions are more important than anything else. Don't eat at a street food stall with no customers, the food has probably been sitting out for a while (and probably isn't very good if no one wants it!). Aim for foods cooked with high temperatures and served immediately. Be careful about mosquitos in dengue regions. Be careful about ice, but ice that looks like it's from a central manufacturer is probably fine (look for the round ice cubes with holes).

I once spent a month in Thailand followed by five weeks in Mumbai without getting sick. Currently in Penang for ten days before flying up to Thailand again, haven't gotten sick yet despite eating all the street food I can find in Georgetown.

The only time I've ever gotten a serious bout of traveller's diarrhea was in France of all places.