Start small and build your business while you develop your plan. Market the dog walking service or grooming or whatever services you want to offer through flyers, posters around town, ads in newspapers. Call the newspaper and maybe they will do a community interest story. Align with the local pet store to get referals and to maybe help them with promoting their business at the same time. Be creative. Maybe start it from your home to keep overhead costs down.

Do get professional help from any number of small business development agencies in your area. I'm from Canada so I don't know how it works in the States but here we can access small grants, a counsellor, support groups, attend workshops etc to help with developing the business plan. You need a business plan to get a loan but you also need a plan to help guide your decisions even if you don't need a load to get started.

Good luck to you. I'm an entrepreneur myself and while it can take years to turn a profit and it will require lots of long hours and a good level of sustainable energy it can be very satisfying to build your own business. Grow it slowly and avoid or limit debt to increase your chances of success.