I taught Daisy how to roll over by getting her to first lay down. She got a treat for that. Then with her still in the down position, I said roll over, with a circling hand signal, and then I physically rolled her over. She got a good girl! and another treat. I kept repeating this, first getting her in the down, then saying roll over with the signal, rolling her over myself, doing the good girl! and giving a treat. After a little bit, she would get in the down position herself, so all I had to do was say roll over with the signal. (still rolling her myself though.)
Soon she would lay on her side for the treat, but was not doing the roll, so I kept helping her, doing the good girl! and a treat each time. Then one time she simply did it on her own! She got a VERY excited good girl!!!! and many treats
I did this over the course of a few days, in 5 minute sessions. I don't think dogs can handle much more than that when learning a trick. Soon they just want the darned treat and aren't focusing on the trick.
What's funny is that sometimes I will have something in my hand that she <span style="font-weight: bold">thinks</span> is a treat for her that she is not getting. She sits nicely at first, but when she still doesn't get it, she will fling her paw in the air to shake and then roll over.