I teach that you should seek to learn from competitors; obviously never copy another business's idea or what they are doing, but you can absolutely learn from their mistakes or see what they are doing and discover ways to improve it. All of that analysis belongs in your business plan: make sure you have your competitors under the microscope and make sure that is a solid chunk of your plan. That is some of the best research and information you will gather about what will make your business successful in future.
Having a business plan is so important to you as an online marketer. But most people, who start online businesses, especially small businesses, do not really take the initiative to make a business plan. Probably they think that it's not necessary. But for sure there is little you can achieve in life without proper planning. More so in the contemporary times when survival depends largely on one's ability to organize your physical and mental resources well. The future is actually for those who are organized. And the future of your business is dependent on your good planning.