By the time you get to high school orchestra, you should be comfortable with shifting. Being able to play in several positions means greater facility in certain passages and increased range on your instrument. The following concepts and exercises will help ensure that your shifts are accurate.
1. Start with correct left hand position
Violin and viola- Your wrist should be straight and your thumb pointed upward against the side of the neck, supporting your hand position. Your hand should be relaxed, not gripping the neck like you're choking the life from it.
Cello and bass- Your elbow should be up and your thumb pointed in towards the back of the neck. Your hand and arm should be relaxed, not gripping the neck like it's a weapon.
2. Shift Correctly
You want your shift to be smooth, fluid, and in tune. Work slowly on making the following three steps occur correctly, then work toward making the shift one fluid motion.
Release- Release the pressure of your finger on the string, but keep the finger in contact with the string.
Shift- Move the hand as whole to the arrival point. The hand should stay in posture as a unit: don't move the finger up then drag the thumb along behind.
Arrive- Stop the shift motion and lightly re-apply the pressure to the string with your finger.
The Hand- Keep your fingers curved during the shift. Don't change your left hand position just because it's moving. The thumb is the anchor for your position. It should always support your hand and fingerings for whatever position you're in.
The Bow- Lessen the pressure on the bow as you are making the actual shift, so as not to "meow" when shifting. In most instances, the shift should be as inaudible as possible.
3. Know where you are shifting to
Envision exactly where your finger will go, don't guess. Think about the distance between your starting location and where you will arrive.
Exercise 1- For smaller shifts, practice hearing the two pitches without a shift, then make it sound the same with the shift. For example, if you are shifting on the A string from B in 1st position up to D, first play the two notes, staying in first position: B-D. Then play them with the shift in between and see if you can make them sound exactly the same: B-(shift)-D.
Exercise 2- For larger shifts, think about where your "anchor" finger will go. First practice the shift by moving to and playing the "anchor" note, then placing down the finger that plays the actual arrival pitch.
Most literature at this level will involve shifting. The more comfortable and confident you are in your shifting, the more you will be free to use the best fingering for every passage, increase your instrument's range, and enhance your playing ability.