practicing doubles has helped alot for my hand speed. tapos nung medyo bago pa ko sa drums, nag-eendurance test ako. continuous singles, doubles, triplets, and/or paradiddles at a given tempo with a set time. if i'm comfortable with one tempo already, i'll speed it up etc etc.
constant practice din, pati trying out new things. speed comes with time, so i never practice with speed as my goal. i practice to grow as a musician, speed is only a beneficial side-effect of that.