Start with an idea of something that you like and can afford to begin doing. Then, think of the costs required to start and keep your business running for at least a year. If you're planning to start something from home with a very small dollar investment, you might not need thousands of bucks to keep it going and if you can't make it work you can more easily cut your costs and move on. You must also account for business license and other initial costs.
Make sure that your home is not in an area that prohibits you from operating a business from home if you will be putting up a sign or having people come in and out. You could be fined or have your business shut down. It is best if you accept credit and debit cards because this can make a significant difference in the revenue of any business. Of course there are many more steps, but you get the idea.