When you research Fiverr before you start, you will see what already sells. See what people are offering, then differentiate yourself from them and sell things that people want to buy.
Working on Fiverr requires you to help people get what they need accomplished. When you are thinking about others, it will make it easier on both you and the client. There are many ways to find out what your potential clients want. See what is selling already, and look at the buyer requests.
Once you have all your research done, then it is time to create your gigs. Make sure everything is clearly written and you describe your services exactly as you are going to perform them. Once you are sure of everything you wrote and you have a clear plan of action, it is time to find the clients.