How to acqure correct elbows position

Hand position determines correct elbow position while descending. Draw an imaginary straight line from index finger to the lower and opposite corner of your palm. Place this line on the handlebar.

Incorrect position:

Correct position (pay attention to the arrow and how it "sits" on the handlebar):

Such hand placement will also assure correct elbow position (as if doing a pushup or holding a basketball somewhere between the chest and belly button. Don't overdo it and don't protrude elbows too much forward. They will not be 90 degrees to the handlebar sticking out straight up. It would be too much). Do the same with the left hand.