When I started off playing, I’d play all sixteenth notes & work my way from high to low. Once I got that good, I’d try bouncing back & forth between two toms, or the snare & one tom. Eventually, instead of straight sixteenth notes, I’d skip some (play an 1/8 or a rest).
The more you play, the easier the flow & more creative you become. Maybe someone else could recommend a good book.