Close your garage door.
Look over the garage door's tracks. These tracks keep the door properly in place and hold the rollers in place. These rollers appear as small wheels and are held in place by brackets. Tighten the brackets by using a Phillips screwdriver.
Check the door's hinges if the door continues to droop. These hinges are located between each section of the actual door and also should be tightened using your Phillips screwdriver.
Use WD-40 to lubricate the rollers and all along the garage door's tracks. Spray a moderate amount of WD-40 directly onto the rollers and tracks. The door will no longer droop.