I want to say this is an excellent post. One thing I would add is that you get a deposit from your clients.

The work I do I ask for 25-35% up front depending on total, remainder on acceptance of final revision/delivery of product. Clients are very loathe to drop out mid-job if they have already put money into you. If the client is not willing to give a deposit, they're likely to not pay you at the end either. The only time i disregard this is with my regular clients whom I bill on a monthly basis, as they have proven to me they can and will pay on time.

Also, as a part of any contract you should state that clients changes are to be billed separately to your initial quote (with your hourly rate mentioned) - so if you deliver what the client wants according to the initial brief, then the client wants to drop this and add in new sections or pages or whatever you're not left being screwed over for your time investment - why should you wear the cost because your client couldn't give you the correct brief in the first place.

Graphic design is a harsh world to be in as there are so many people out there willing to screw you over because your work is digital not physical so it doesn't have as much perceived value, so protect yourself!