This article is from the Fitness FAQ, by Jeff Gleixner (glex@cray.com) with numerous contributions by others.
Basic Form: Keep wrists straight. Don't rock backward. Flex biceps
at the top. Keep elbows down and against the ribs.
BARBELL CURLS
Set-up: Standing, using a shoulder width, palms up grip on barbell.
Barbell resting on the upper thighs, arms straight.
Movement: Lift the bar in a slow, steady arc toward the shoulders.
Raise until forearms are almost verticalthen lower the bar in
a slow arc back to the starting position. Keep elbows and upper
body motionless. Keep elbows level with, or in front of the
body.
Variations: EZ-curl bar will place less stress on forearms.
Dumbbells - Start with arms at side and rotate hands until
the hands face the outside bicep area at the top of the
movement.
Cable Curls - Same movement. Use machine with a low pulley
and a straight cable handle.
To avoid cheating try them with the upper back against a wall with
heels about 1 foot away from it.
Muscles Worked: Biceps, brachialis, forearms.
PREACHER CURLS:
Set-up: Seated on the preacher bench with a slightly wider
than shoulder underhand grip on barbell. Lean into the
preacher stand, firmly pressing the upper-pectoral muscles
against it.
Movement: Lift bar slowly upward in an arc until it almost touches
biceps. Keep upper arms on the pad and don't let the elbows
spread apart.
Variations: Use EZ-curl bar, dumbbells, or a low pulley and
a straight handle machine.
Muscles Worked: Biceps (lower), forearms
HAMMER CURLS:
Set-up: Dumbbells held at sides with palms facing the body.
Movement: Raise the dumbbell as far as possible without
allowing the elbows to move. Keep the palms facing
the body throughout the movement.
Variations: One arm at a time or try them seated.
Muscles Worked: Biceps, forearms.
 
Continue to: