LISTEN, LISTEN, LISTEN!!!
Practice slowly and legato. Match open strings. Find fourths and octaves. Listen for the ring. Use the drone for difficult keys (such as those with flats in them).
Plan your finger patterns. If the passage is fast, “hover” when ascending and have fingers already waiting when descending (even though this will not be perfectly comfortable at slow tempos). Always work in the grid.
Anticipate string crossings – left hand arrives before right; sound the doublestop.
Slur across shifts; play the note before the shift, slur to the note after the shift, repeat that note and slur as you return to the beginning note. Release before you move. Also practice hitting high notes from nowhere. Is your left elbow in the proper alignment? Where does your thumb need to be?
If you are playing moving notes under a slur, practice high lifts and drops; then play through with electricity in the fingers, but keep the fingers close.
If you are playing separate bows, you do not need as much action in the finger; be gentle. The rule is: for the start of the bow or on a string crossing, the action is in the bow, and the left hand relaxes; when the left fingers articulate under a slur, the bow is quiet and the left hand is active. You can reduce much tension in the left hand this way.
Remember that fast playing is light playing on the fingertips; slow playing transfers weight from the arm (just a bit) and feels deeper, and vibrato helps enormously to keep things loose. Do you have a footie?
For high notes, find the balance and the C shape; alternate popping the finger and releasing to the open string.
Play scales releasing to open strings or harmonics to reduce tension and gain speed.
Practice the necklace technique – play one beat plus one note really fast; repeat; play the next beat plus one note really fast; repeat; then string the two beats together. This is particularly helpful for coordinating bow and left hand in fast passages.
Practice in rhythms – long, short short short long, etc. Keep the bow arm relaxed.
Practice with the metronome and line up the left hand exactly. A good technique is an even technique!
Sounding Point and Relaxation
Watch your sounding point, especially on bow changes. (A mirror can be useful for this – watch the shape between the bow and the bridge.) In general, keep a steady sounding point.
Practice in the part of the bow you will be using. Mark it if necessary (LH for lower half, eg.). Try to use the same amount of bow as well. Use the correct part of your arm.
Keep a steady sounding point when working on technical passages. Make as beautiful a sound as you can. In general keep a steady bow speed; keep your arm smooth and avoid jerks or lunges.
When working on a melody, consider bow angles needed to avoid false accents. Mark FA (frog away) or FI (frog in) if you notice a blemish in your line.
Put yourself on a metronome diet; practice with subdivisions, marking them if necessary.
The necklace technique is also helpful for the bow.
Accent string crossings for slurred passages, but do this with speed, not tension. Practice legato doublestops, pivoting smoothly, for lyric melodies.
The character of the passage will ultimately determine whether you want clear bow changes or smooth, but usually when learning a technical passage, clear is better.
Write in dynamic shapes (microphrasing), especially in Bach. Even adjectives describing character will help.
Make the phrase first with just the bow, then with just the vibrato, then with both.
Mark difficult passages with a star in the margin. When you have five minutes just do the stars!
Analysis and problem-solving are the heart of your work in learning a piece. The pace at which you can learn will depend on how difficult the piece is in relation to your technical level. If most of the piece is at the very top, or beyond, what you are easily able to sightread, you should expect to spend many hours of slow work before playing it up to tempo. Take whatever time is necessary to work on each page of music. Slow is better; even though it feels at first as if you are making no progress, if you are really practicing with understanding, things will start to snowball, and you will not only sound better, you will have an unshakably solid technical foundation.