Here's how I learned this past summer. I'm still working on it but I'm getting there. Just start by doing a 90 degree turn with one roll involved. do it both ways and get used to what your fingers are doing. Once you get the feel for it start doing 180 degree turns, you get the idea. Many people will say that rolling to the outside is easier, and in my limited experience I tend to agree, but when I started it was easier for me to 'think' my way through rolling to the inside. I have found to make good rollers, you need to use lots of rudder, a low amount of elevator, and very little aileron.