The best time to be sure a sliding patio door is properly adjusted is before it starts sticking in its track or hopping out of it. All it takes is a few turns of the adjusting screw on the edge of the bottom rail of the door.
To check the adjustment, stand back and look at the door from the outside; there should be a uniform gap along the bottom and top edges of the door. If the side with the adjusting screw is too high, causing it to bind at the top, turn the screw counterclockwise. If it's too low, use a flat pry bar to raise the door while you turn the adjusting screw clockwise. Regular vacuuming of the track will help keep the door sliding smoothly. Never lubricate the track, however; the lubricant will attract dirt.