Warning: There are hot surfaces, chemicals and possibly ill advised actions like you would expect in many Instructables here. You will also be running tape and un-approved paper through a laser printer. There is a very real danger of messing up your printer. If you do wreck a printer please comment so we can all learn a valuable lesson.
There are some good Instructables on using toner transfer, but after doing my own for a while I have some refinements on the process that I want to share. You should be able to create high-quality, well aligned double sided boards every time.
If you are just dealing with a basic board for 0.1" pitch through hole components this is probably overkill. A good instructable for those kinds of boards this one by pinomelean.
UPDATE: Sad because this won't work with your Brother brand printer? fmarquis to the rescue with a PCB's flamethrower style Instructable.
I have made excellent boards with 8 mill pads and 12 mill clearances.
There are a few secrets. 1. a laser printer. 2. a hot laminator. 3. (The big secret) Parchment cooking paper. 4. Careful and diligent cleaning of the board.
If you follow my directions to the letter you can get great results.