Most leopard geckos will only eat live prey, and they'll feed on a variety of insects including crickets, locusts, mealworms, silkworms and waxworms. Usually, keepers choose crickets as the primary staple diet as they provide a good balance of nutrients, while protein-rich locusts and silkworms should be mixed in occasionally. Waxworms are very fatty and should be fed only once or twice a week as a treat.
Hatchlings and young geckos should be fed between four and eight food items per day until they reach adulthood, when this can be adjusted to five to ten items every two or three days. As a general rule, feed your gecko items that are no more than the length and less than half the width of the head. Hungry crickets have been known to take a nibble on geckos while they're sleeping, so leave a bit of grated apple or carrot in the vivarium for any uneaten crickets.
Live food should be 'gut loaded' to improve its nutritional value - you can do this just by putting fresh fruit and vegetables in the crickets' box for them to snack on. Take care with the cricket box and remember these insects are natural jumpers - you might get a few escapees from time to time! Check the vivarium regularly and remove any dead crickets: your gecko probably won't eat them but live crickets might, which can increase the risk of disease.
Supplements are another important part of your leopard gecko's diet - use vitamin and D3 powder once or twice a week, and a calcium-only powder every day. To dust your crickets, simply put them in a plastic bag with a small amount of the powder and shake it! You can also provide a dish of pure calcium powder in the vivarium so your gecko can help itself when it wants.