You start with a setup board, or a very flat surface. Then you get a Tweak board/station like the ones sold by MIP or Integy (make sure it's for 1/10 scale touring). Then you follow this writeup:
Here are some pics:
These are very simple devices. You put the center bar and rear bar together. You adjust the three feet to level the center & rear bar (using the front bar as a level). Then the front bar is slipped onto the center bar. The front bar is free to pivot left & right displaying the tweak of your setup. After you center the car on the tweak board, you start work on the front end. To do this, you place the rear of the car on blocks (actual ride height with tires removed is best). Now you adjust the front spring collars until the front bar becomes level. Once this is done, you work on the rear by removing the blocks and setting the rear tires on the block. This then causes the front bar to tilt again displaying rear tweak. Now you adjust the rear spring collars until the front bar becomes level again and your done.
Any adjustment's after that will effect tweak, so it should be the last thing you do. According to that writeup, many pro drivers check & adjust right before every single run...