Thanks guys. I think my technique is fine, although I do sometimes take the racquet too far back.
It's just that I seem to struggle outside of practice because the balls that come at me aren't always close and easy. They're out of reach a lot or I react too slowly to get my racquet on them.
That may be because I don't hit a good approach shot sometimes, but I have a friend who can pretty much come up to the net any time and put balls away with ease.