I have only been doing it for about 2 months now and these are the things I have learned,
1. Be patient with yourself and clients. Don't expect to know everything the first day.
2. Remember to stop and take a break. Go outside. Turn off the pc, phone, and shut out the whole electronic world for a little while each day.
3. Keep yourself organized. Make notes on each project and put it in the folder for the client along with any contracts or sketches.
4. Don't take on more than you can handle. Don't be afraid to say no.
5. Let yourself accept the criticism you get from the client. They may make you feel like you are worthless, but they have an idea in their head and may not know if its even possible or how to describe it. Take the criticism, keep it in mind and keep moving forward.
Hope this helps someone.