I am looking into this at the moment because I am getting married in October. I came across an article in a wedding magazine with exercises in it.
One was to hold cans of beans in your hands put your arm up and drop it down behind your shoulder then raise it up straight again, it said to do 30 reps at a time.
Another was to get a kitchen chair and do what I think of as backwards press ups. Facing outwards put your hands behind you on the edge of the chair, legs out at a 45 degree angle and raise yourself up and down using your arms.
I can't remember anymore off the top of my head but good luck with it : )