If you are on final with 40 degrees of flap and you have to consider side-slipping to lose height, then its probably time to throw away that approach and start again. Practise make perfect. Start by treating every landing as though on a short strip, use the numbers from the POH and stop adding a few knots on for good measure. As you gain in confidence and experience you can, with the owners permission, start visiting some of the more challenging strips such as Hardwicke, Stancombe, Eastbach etc.