If you find marketing and selling yourself disagreeable, you're not going to do as well as an independent contractor as you might. Sign on at agency which supplies technical writers. With an established reputation for doing good work and a solid network of people to refer work to you, you may decide to leave the agencies and contract for work on your own. Peter notes this may take anywhere from a few months to a few years, or some technical writers may find their own comfort level in working for agencies. Moving from using agencies to contracting for work yourself gives you, in effect, a raise.
Clients usually know the going rate for contract technical writers.
If you contract for the work directly, you get to keep the full hourly rate without leaving any of it in the hands of agencies. The next big step is to start charging for your services by the project rather than by the hour. You are then a consultant. Your income goes up because your rate of pay will depend upon what the competition charges, not the going hourly rate. The advantage here is the better and faster you work, the more money you can make.