One of SharonA's tips is _SSOOOOO VITAL_ that it bears repeating:
If you "mess up", don't stop! Keep singing the song and let your strumming hand find the rhythm again.

If, while practising, you stop the song, what you are practising is stopping, which is waaaaaaay counterproductive.
40 years of pickin', learned this lesson late. :(

One other observation is about distributed versus massed practise. Fifteen minutes a day every day will produce more results than marathon practises once a week.
I can distinctly recall thinking I'd never be able to sing and play together. ermintrudeclaire, you _will_ get it. You've got a trove of tips from this thread and I wish you joy in your music.

Dennis