Pet sitting prerequisites are pretty loose. You do have to enjoy interacting with animals, or your pet sitting career won't work out well for you or the animals. It's best if you don't have any serious pet allergies, as the constant fur and dander may give you more trouble than you bargained for. Beyond that, it's helpful if you've had some previous positive interactions with the species you'll be visiting. You might be comfortable with dogs' wide-open, slobbery greetings, for example, but find that cats' unpredictable nature intimidates you. In this case, it's perfectly acceptable to limit your services to households with canine members. However, don't be surprised if you don't get an invite to the National Feline Convention in D.C. in September.
Of course, you can always prepare for your pet sitting career by racking up some volunteer animal handling time. Your local animal shelter will probably welcome an extra set of hands to socialize the facility's dogs and cats. The shelter staff might even allow you to share in the pooper-scooper and litter box patrol. Now there's an added bonus.
Consider clocking some hours as a grooming shop bather. You won't make much, you'll be sopping wet after wrestling with animals of all sizes and athletic abilities, and you’ll smell like wet dog. But you'll likely become a more competent handler—which adds to your pet sitting skills. If you can expand your expertise to grooming talk show hosts, you may even become a qualified Chelsea handler.