A good accountant is a great idea. If you are new to running a business then it will be really beneficial to have someone to help you with the financial side.
My tips would be
1. Advertise on the internet. People use the internet more than anything these days to get what they want, Make sure you are right up there in google when people in your area search for gymnastics, children's activities or anything. People like it to be easy nowadays they don;t want to go out and search or follow up ads. They want to google something, and have a nice easy page where they can send an automatic enquiry and set it all up without getting off their chair.
2. the key with the current population is to get the balance between fun and serious. Many parents want it to be a fun, laid back, once a week activity but they still want their kids to feel like gymnasts.
3. Set up a program with lots of rewards and incentives, make small progress special, reward it. This helps kids feel like they are progressing, and parents want to see this too.
4. Hold events, if you are a recreational club its important to hold events, even small ones are great. Kids who don't compete don't always feel like they get to do anything with their gymnastics. Specials displays or fun in club competitions help with this.
5. Do it yourself. It takes a long time for a new gym to turn a profit. I have seen new gyms hire to many staff to start off with and they have lost everything. Teach the classes yourself until it becomes too big to do this.
6. Believe in what you are doing, people will see this and they will put their faith in you.