Here are his tips for aspiring free agents. Only take work that teaches you something new. You don't have the time to deal with a job that rehashes something you've done over and over. To enhance your portfolio, you've got to keep learning and expanding your repertoire. Take work that will lead to more work.
Some employers simply generate more work than others.
Look not only for big companies that may refer you internally, but for companies with wide networks of shops they could refer you to. And think twice before turning down a high-profile project, especially an interesting project with a prestigious firm. If the prestige attracted your attention, it will likely attract others' too. Fun is an important metric. One important measure of any job is your enjoyment level.