It's been a while, but this is what I did for trailers:
Oil or Wd40 while on ground.
Mark chalk line across spring and one nub(for counting turns).
Install bar/springs on wall.
Lift door overhead leaving gap, and keep in place w/vice-grips on track.
Attach cables and turn onto pulleys until snug, even and aligned.
Tighten all pulleys etc.
-Door is now mostly preloaded.-
Lower door.
Finish last few turns of spring.

You'll need a stable ladder and a big pocket for the wrench and bars.

My dad needed plastic surgery to the back of his hand when tried to DYI his garage door spring.