Detach the cable from the mech.
Set the shifter into the highest (hardest) gear.
Check that the limit screws don't allow the chain off the end of the cassette or into the spokes (move the mech in and out by hand whilst turning the pedals).
Get the mech into the highest gear position (its natural position without a cable attached).
Wind the barrel adjuster all the way in (clockwise).
Attach the cable to the mech as tight as you can get it.
Shift down one gear whilst turning the pedals.
If the chain doesn't move onto the next sprocket, wind the barrel adjuster out (anti-clockwise) slowly whilst turning the pedals until the chain goes to the next sprocket.
Go down another gear and see if that shifts.
Tweak barrel adjuster to suit until it all runs sweetly.
Set the shifter into the highest (hardest) gear.
Check that the limit screws don't allow the chain off the end of the cassette or into the spokes (move the mech in and out by hand whilst turning the pedals).
Get the mech into the highest gear position (its natural position without a cable attached).
Wind the barrel adjuster all the way in (clockwise).
Attach the cable to the mech as tight as you can get it.
Shift down one gear whilst turning the pedals.
If the chain doesn't move onto the next sprocket, wind the barrel adjuster out (anti-clockwise) slowly whilst turning the pedals until the chain goes to the next sprocket.
Go down another gear and see if that shifts.
Tweak barrel adjuster to suit until it all runs sweetly.
