A diet of crickets, supplemented with other insects, is fine for tarantulas. An adult need to eat surprisingly little - certainly not daily, and once a week may be sufficient. Some owners may try to mimic how a spider would eat in the wild - e.g. completely randomly (maybe a couple of crickets, then one cricket several days later, then a few crickets a week after that, and so on). Adults may fast for extended periods (a month or two is not unusual), particularly before a molt. Growing spiders, however, should be fed several times a week.
The cricket should be gut loaded prior to feeding - that is they should be kept on a diet of nutritious food, and they can also be dusted with vitamins prior to feeding. Remember that what goes into the cricket is what you are ultimately feeding your spider. Meal worms, super worms, and roaches can be fed occasionally. Larger tarantulas can even be given pinkie mice and small lizards, if desired, although it is probably not necessary. The most important thing is to keep the food smaller than the tarantula (that is, smaller than it's body) and make sure the tarantula isn't harmed by its prey. This includes not feeding any wild caught insect unless absolutely certain there is no risk of pesticide exposure. When molting the spider is very vulnerable and even a cricket can kill the spider, so remove any uneaten prey within 24 hours at most.
As mentioned in the housing section, a shallow dish of water should also be provided. Pebbles can be placed in the dish to ensure that the spider cannot drown (and also to keep prey insects from drowning).
This is how the spider grows to a larger size - by shedding the old exoskeleton and producing a new one. This is a stressful time for a spider and this is also when humidity levels are most critical. The spider stop eating for some time, then will lay on it's back to molt. The molting process may take several hours. Once the old exoskeleton is shed it will take several days for the new one to harden (this is when growth occurs) and the spider should not be fed during this time as it is vulnerable to injury and even death from something as small as a cricket. In addition, the spider should never be handled during the molting and hardening time. It may take up to two weeks for the spider to fully recover after molting.
What About Handling?
While most tarantulas are not very venomous many tarantula experts advise against it. For the handler, bites can be painful, and irritation can result from contact with the itching hairs on the tarantula, but the greater danger is to the tarantula itself. While a tarantula may become acclimated to being held on the hand, if it suddenly runs or jumps it may fall, and the injuries sustained could be fatal. Even a minor fall can kill a heavy bodied tarantula if the abdomen ruptures. Some tarantulas are very fast, and could escape as well. Children should not be allowed to handle them, due the risk of injury to both the child and the spider.