This infographic covers common errors people make in their freelance career that you should avoid. From Creative Market, 'Five Mistakes Every Freelancer Makes' will be especially useful for people trying to build a successful design practice. However, even through failure, invaluable lessons can still be learned.
The first error to avoid making in your freelance career is not knowing when to say no. Many people take on every job or additional task from clients. Trying to appeal to everyone is a bad idea. Instead, specialize in one or two services and create a niche for yourself. Working too much will result in burnout. This is something you can't afford, especially if you aren't charging enough for your work. You should also use a formal contract.