My philosophy is to simplify things as much as possible. Help players make one or two positive adjustments in their defensive techniques.
Most players routinely make basic mistakes.
Focus on the fundamentals. One key area that doesn't get much attention is foot work. Have players add a jump rope to their equipment and have them use it a few minutes as part of warm-ups and between practices. Another key, which many coaches and players choose to ignore, is muscle memory. The only way to develop muscle memory is through repetition - practing over and over and over.