The best way to make your strokes fast is to start out with 2 strokes each hand. 2 Left , then 2 right. Start out slowly then gradually quicken the pace until it sounds like a roll. Then you can always move up to 3 or 4 strokes each hand. And if you can do more to the point of which it sounds like a roll than do it. But that's the best way to increase your drumming speed in general