I have been a freelance writer for more than 11 years. I started out writing articles for print mags and now I do mostly web writing with a little print.
I've found that the best formula for me is to have around 1/3 of my income be residual. This allows me to still be making money even when I take a day off, which is important since I have health problems and two young children.
Also, I think it is important to have as many clients as possible at one time and to be continually looking for new clients. I've found that 90% of clients disappear, go out of business, etc. after a few months and you need to have another in the pipeline. This is incredibly important if your family relies on your income.