Grab a barbell with your hands shoulder width apart, and arms nearly fully extended, and at your sides, as shown in the picture to the right. Make sure to be nearly all the way down but, never all the way down such that you are locking out your elbows. Inhale in this position.
While keeping your upper arms planted at your sides so they don't move, flex your biceps to raise the barbell until your forearms are at about the 10:30 position on a clock (if you bring the forearms any higher, then your upper arms will start to raise from the sides of your body). Return to the start. Repeat for reps. Keep your abs and glutes engaged during the movement to help keep your body stationary. Keeping your body stationary will keep you from cheating during the exercise.
See movie showing the exercise:

Biceps Exercises:

barbell curl	dumbell biceps curl	machine preacher curl
biceps incline curl	dumbell preacher curl	preacher curl
cable biceps curl	dumbell reverse curl	reverse grip biceps
cable preacher curl	dumbell reverse preacher curl	reverse grip cable curl
cable side biceps curl	hammer curl	reverse preacher curl
concentration curl	machine biceps curl