My (overly brief) summary/adaption/commenting:
- It's a passion, not just some job. {Write|Design|Program|Model|Work-on-it} every day. Manxy of us freelancers love their work, and spend loads more than 40h/week with it. When asked "what's your hobby", "work" is very often contained within the first three to five answers (my answers are "family, sports, work, food", with family first and the others in no particular order)
- Market yourself - don't wait for opportunities, create them!
- Work with more than one client at a time. Lowers overall risk, increases usefulness for a single client as you bring in experience from multiple other sources.
- Have a niche, sometimes called USP (unique selling point). You may even call it professional hobby, as that's what it is in my case (currently there are at least two of them, arc42 and rule-based-systems.)
- Have a website. I do not understand freelancers and entrepreneurs in the IT sector who currently do not maintain their own. But there are such folks around...
- Remain hungry: be consistent marketer. Speak at conferences, write articles, books, blogs open-source software. Ensure the market does not forget about you.
- Long ago we stopped working 40h weeks. See point 1 - it's a passion. A familiy is always around, so is your enterprise. As long as you feel in control of your life, you're living your life your way, it's ok to work longer hours.
- Maintain active and symbiotic/synergistic partnerships with others of your kind. Treat them as equals and friends, not a contenders. Support their search for appropriate projects - and they will in turn support you.
- Give away freely. Give your books to your clients and prospective clients, contribute to open-source projects, create free whitepapers and the like. Readers will love it and come back to you, maybe even years later. If your stuff is good, people will remember it! (thx to Jerry Weinberg for this valuable hint!)
In my humble opinion you should add the following:
