I can bowl accurately and keep a good line. I tend not to drop short but I bowl too many half volleys.
What things might I need to think about?>
It's all about the point of release. If you overpitch you are letting the ball go a fraction too early.
Be careful not to over-compensate. I would much rather a spin bowler bowl half volleys than long hops: you can set a field to deal with a regular half-volley, long hops can go anywhere.