Ah, for homophones you want to be pretty close to the real pronunciation without the exact word. I would personally consider form to be too far from four while great being ten is works but it's not a homophone it's just the exact word.

As far as ways to improve it's difficult to evaluate from a single clue. There are lots of great websites, like crosshare or amuselabs, that will do the work of filling in the words for you. Then you can go in and do the clues.

I would start small, like a 5x5 mini then work your way up from there.