- step into the ball, closed stance (i.e. sideways)
- use high takeback, hit across the body to impart both side and backspin
- hit only slightly in front of the body (less in front than in a normal backhand)
- swing non-dominant arm towards the back parallel to the baseline to keep balance
Disclaimer: I'm NOT a coach...
Real tennis: https://www.youtube.com/watch?v=yDqnkLJ9BtM