I've read some great ideas. Here are a few things I have done.
I never talk to him as a male, it's girl,her, she ect.
In addition to diapers, I keep her locked up in a chastity lock.
Keep her dressed as a girl whenever possible. When it's not possible, I'll still have her wear something femminine a garter belt and silk stocking, or panty hose ect.
Make her totally dependent on diapers. This takes time but worth the effort. If she gets out of line, remove the diaper and theaten to take them out some place crowded like the mall.
Change her in front of friends. I'll change her in front of my best friend and her husband all the time. And if you really want to humiliate her, I have her pleasure him orally.
This is just a short list, but I look forward to trying some of your ideas.