One of the goals of every freelancers is learning how to make the clients happy. Ensure that you are working towards satisfying them first. You don't need to focus more on the profit you need to make first. That will naturally come. You as well need to be sure that you are only handling task that you know much about. You don't need to be handling tasks to impress clients or because you need money. Then learn how to talk to them politely even when they are wrong.