If you constantly struggle to hit your backhands aggressively, and never quite feel like you can hit through the ball, one drill I like to do to get myself in an aggressive mentality is to practice touching my right shoulder to my chin on the preparation phase, and after I hit the ball, touch my chin with my left shoulder on the follow through.
With each backhand, the physical contact of right shoulder / left shoulder will give you immediate feedback as to whether or not you are (a) turning your shoulders properly and (b) hitting through the ball.
It may feel different at first, but like Agassi’s dad used to tell him – ‘just keep whacking that ball hard and one of these days it’s going to go in’. But in all seriousness, it will help you break through the mental barrier of having a ‘weak’ backhand, and help you feel like you can attack the ball from both sides.
Check out this slow mo of Djokovic – 36 seconds for the right shoulder touch, and 2:40 for the left shoulder touch. https://www.youtube.com/watch?v=Ed3S-X1Xiv4