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.
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.
Sad because this won't work with your Brother brand printer? fmarquis to the rescue with a PCB's flamethrower style Instructable.
Some brands of Parchment must be cleaned with 99% isopropyl alcohol for the toner to stick when printing. My HP1102W needs this or else the toner flakes.