Your instrument is safest when you are in 'rest position' or in 'playing position.'
How NOT to carry your instrument: The bridge is NOT glued on very easily broken if you pick up your instrument by the bridge, strings alone, fingerboard, tuning pegs and tail piece.
How to carry your instrument:
Violins / Violas: By the neck and shoulders of instrument. Safely tuck it under your right arm behind the bridge, making sure not to squeeze the bridge out of place).
Cellos / Basses: By the neck of the instrument with the addition of using the waist of the instrument to balanced the weight. Always carry your instrument in front of your body -- I recommend sideways to make your profile more narrow.
Here we see some advanced shifting. The arm is comfortably wrapped around the neck and body of the instrument.
Keep your pizzicato hand relaxed.
German bow hold. Cradle the bow gently.
Pizzicato hand position. Notice how the bass arm and elbow is elevated off the shoulders and neck of the bass.
Rest position in bass.
Notice the bass arm is NOT resting on the back of the instrument. The bass arm is free to move as needed from position to position and string to string.
This is a French Bow with a French Bow Hold.
Notice how straight the cello wrist is. The bow hold is relaxed and poised.
Cello Rest Position
Excellent bow hold.
When pizzicato playing is happening you can hold your bow in rest position with the first finger and thumb free to pizz.
Here's a great example of shifting and playing in thumb position. The elbow is free to move up and down the fingerboard.
Extending your arm for full bow use needs to stay straight and inline with the end of the fingerboard and bridge.
Look at the nice bow hold. Relaxed and ready to pull
When your bow goes up towards the frog, the wrist relaxes to accommodate the tight area.
A great view of shifting position with your thumb, hand, wrist and arm all working together
Straight bows create the best tone.
Rest position with the viola.
Notice the way his arm and elbow swing under the viola to reach the notes on the C string.
Notice the relaxed bow hold. The knuckles are down and not raised up like a 'backbone.'
Here we get a great view of how open the bow hold is. See all the space and roundedness of the hand?
Casual Rest Position
Here's a great example of a straight violin wrist. The bow is also 90 degrees from the fingerboard and bridge
Violin rest position. Always point your bow down.
Keep your nose in line with the fingerboard and scroll.