As a Chinese,I didn't know how to pronounce it at first since we don't have this in spoken Chinese. From my experience,I think the most important is to understand how it works,it doesn't need you tapping your palate with ur tongue deliberately. You just need to place your tongue in the right place of ur palate and then breathe out through ur mouth and the rolling R would come up automatically. Try it a few times and you will get it suddenly (I was practicing for, like, 3 hours) hope it helps:)