Groove the half-volley. With a slow, high serve, set the feet, watch it drop, and strike it clean on the half-volley.
A higher, slower serve gives the striker time to set and strike the half-volley on the drop. Emphasise setting the feet early, watching it onto the foot, and a clean contact. Build to a firmer, on-the-run serve. Rotate.
Fork it into your private drills, then change the animation, adjust positions, swap equipment, or drop it into a session block.