Hi pasta - sorry, I was in a hurry this morning and missed this. (out cat-sitting!!). I actually work with a friend. It's her business but I started helping out several years back and now I do a large part of it as she has been very ill. She started out by advertising through local vets, magazines and word of mouth. I would suggest you start by seeing what is on offer locally, how much they charge and what they offer. I go in to people's houses and feed and play with the cats plus clean litter trays etc. You also need to be confident about medication - I have even had to give a diabetic cat his insulin injections which is not as hard as it sounds. I also water plants and look after other small animals like hamsters, rabbits and guinea pigs plus the occasional budgie. It helps to have an understanding of animals' needs and to really like them of course.
I would suggest you talk to your vet and maybe put a few fliers round through doors to try to guage the need. But be warned - it sounds like a cushy number but it can be very demanding and you need to be available at all times of year including Christmas so it can be a 7 day a week, 52 weeks a year job. That said it's great fun if you love cats but don't expect to get rich on it. Good luck - if you need any more information let me know