While rear derailleurs may look complicated, they are actually quite simple to adjust. Most derailleurs have three adjustment screws, and rarely do all three need to be adjusted at one time. Often the only time you will need to adjust the groupset derailleur is when it is first installed, although there are times, such as when the hanger bracket gets bent, that adjustments will be necessary. Derailleurs should also be adjusted whenever you replace the chain.

1. Shift to the largest sprocket. Turn the corresponding screw (usually the lower screw in the pair, or the one labeled "L") counterclockwise to move the derailleur toward the bike frameset, or turn it clockwise to move it away from the frame. Align the derailleur with the largest sprocket.

2. Shift to the smallest sprocket. Turn the corresponding screw (usually the upper screw in the pair, or the one labeled "H") counterclockwise to move the derailleur away from the bicycle frame, or turn it clockwise to move it toward the bike frame. Align the derailleur with the smallest sprocket.

3. Shift to the largest sprocket. Adjust the angle of the derailleur by turning the b-tension screw. Turning it counterclockwise moves the pulley closer to the sprockets, while turning it clockwise moves it farther away. The pulley should not rub against the sprocket.
 
4. Shift to the smallest rear sprocket and largest front sprocket if your bike has rear indexing. Increase tension by turning the barrel adjuster (where the cable comes out of the derailleur) counterclockwise in quarter-turn increments until you can shift into the second smallest sprocket.
 
5. Shift to the second smallest sprocket. Spin the pedals and turn the barrel adjuster counterclockwise until the chain scrapes on the next largest sprocket.

6. Turn the barrel adjuster clockwise in quarter-turn increments and spin the pedals. Repeat until the chain no longer scrapes.
 
7. Shift to the smallest sprocket. Spin the bike pedals and shift to each larger sprocket. If the chain scrapes in any gear, turn the barrel adjuster clockwise in quarter-turn increments until the scraping is eliminated.