With a catering business, you have a large resource of potential customers. The hard part may actually be narrowing down your "target market" to focus on a particular niche - will you be catering large corporate events? weddings? small private parties? family dinners?
Start by deciding what you like best - and when you like to work (weekends, evenings, holidays, Monday-Friday...). Make your business one that you'll truly enjoy. Then you can focus on meeting the needs of your particular clientele.