Step One: Raise your left arm as if you are about to play the bass and touch your shoulder with the tip of your middle finger, almost like you are going to flap your arm like a chicken wing.
Step Two: Using your wrist as a guide and your middle finger as a pivot point, move your forearm from the elbow slowly and smoothly up and down.
Step Three: Once this motion begins to feel comfortable and fairly controlled, it is time to try it on the bass. Start by using your second finger in a position and on a string with which you feel very comfortable (remember to keep your first finger down as well). Make the same motion as above. If it doesn’t feel right at first, move your hand away from the bass and try it on your shoulder again. Move back to the bass and try again. Keep doing this until you feel comfortable vibrating on your second finger.
Step Four: Try it with your first finger. If it doesn’t feel right, move back to the second finger. Once it is comfortable again, move back to the first finger and try to maintain the same feeling and control you have with the second finger. When you feel comfortable with the first finger, do the same thing with your fourth finger.
Step Five: Now it is time to move to other positions. Once again, start with your second finger in the position and on the string with which you began. Shift to the new position and vibrate with your second finger. If it does not feel right, move back to the original position and vibrate there. Move back to the new position and try to maintain the same control and feeling you have in the original position. Keep repeating this until you feel comfortable vibrating on your second finger in the new position. Now do this with all of your fingers and in any position you wish. Then do the same thing on all of the other strings.
Step Six: Do not expect your vibrato to change over night. It takes a lot of time and patience, but the payoff is well worth it.