Courtesy of IntownBicycles on Youtube
Instructions
Limit Screws : The low screw affects how the gears go down and the high screw affects how the gears go up. Adjusting the high screw also affects how far the derailleur can go out, which can help with how fast the gears shift. Adjusting the low screw affects how far inward the derailleur goes with the chain. If the derailleur is too far in, it will bump into the wheel, and can cause major injuries to the bike or you.
Barrel Adjusters (on the derailleur cage) : If your derailleur shifts hesitantly, adjust the barrel so that it is able to move more crisp. Make sure that the pulley wheels are aligned to the cog that the chain is on. Also make sure that as the gears go up or down, that the pulley wheels are still aligned with the cog. To check if you've done it correctly, move through the gears rapidly. If the moevment is crisp, then you have done it correctly.