This is what I do, and have had success with it. I dust my feeders with repti calcium WITH D3 three times a week. Monday, Wednesday, and Friday. I leave a small water bottle cap full of repti calcium WITHOUT D3 in the enclosure for him to have as needed. Leopard geckos can tell when they need calcium and will eat it themselves, and while it's rare for them to overdo the calcium, it isn't for them to overdo D3, which is why I leave the calcium without it out in the little cap.
As far as vitamins, once a week, usually on the weekend, I will dust a mealworm or two with Reptivite, which is Zoo Med's multivitamin.