Jo King - Welcome aboard. I wasn't sure from your initial post if your request was about rhythm patterns or timing problems. Timing problems can be helped by the use of metronomes, but I find the "rhythm box" solution easier to take. A lot of electronic keyboards have little rhythm generators that can be use to establish a beat that you can play to. You punch the "bossa nova" button and an easy going latin groove is laid down which you can play against. This can help both timing and rhythm pattern problems.

Some folks have problems finding a comfortable strumming or picking pattern to fit a song or song type. My suggestion about that is to listen to recordings of songs that have a similar rhythm, by good guitarists, and imitate what you hear. Don't worry about following chord patterns, necessarily. You want to listen for up strokes and down strokes (which can be tricky to discern), trying to make what you're doing sound "just like the record". Richie Havens is as strong a strummer as you are likely to find. Pickers like Doc Watson or Tony Rice are great for individual note stuff. It all rests on what you want to sound like; different strokes for different folks really does apply here.

I'm sure that there must be some video or audio tapes out there that you can refer to. And there is always the "how did you do that approach", when you see someone who played the way you like.

Wish I could be more helpful. A lot of practice (woodshedding) goes in to playing good rhythm guitar. It is a much undervalues art.

Good luck
Bart