Lift the garage door up once the spring is in place. Put vise grips or c-clamps on the track on each side of the door to keep it from falling down.
Take the end of a steel cable and climb onto a ladder in the garage door opening. Feed the cable over one of the pulleys that is near the bend in the track. Hook the end around the small knob attached to the side corner of the door.
Climb off the ladder. Carry the other end of the cable to the top of the garage door. Climb back on the ladder and thread the cable around the pulleys near the spring.
Pull on the cable to create less slack. Weave the end through a small bracket in a "figure eight" manner to secure it.
Hook an s-hook through the bracket. Carry the s-hook to the door opening.
Climb up the ladder again the attach the s-hook to the track, near the bend. Stick the S shape through one of the holes in the track.
Repeat the above steps to install a garage door cable along the other track.
Install a safety cable through each of the two springs. Secure the ends to the brackets.
Remove the vice grips or c-clamps and lift the door up and down to test the spring tension.