What service should be taken seriously by new freelancers?

[Btaliat]

With good mentors, there are much advice that will be rendered to freelancers. While all these advice should be reversed and taken seriously, there are some that you may not take that serious. For instance, you need to know that freelancing comes with its own difficulty. You should know that your clients matter. You should know how to take care of them. These should be more emphasis on some of these advice. What other ones do you know?