One of my favourite ways to increase hand speed and dexterity is by practicing the 6-stroke roll. In my opinion it's one of the best sounding rudiments and is by far the most fun to play. The exercise I've provided below incorporates all four different variations of this rudiment into a 4 bar phrase.
I strongly recommend moving this exercise around the kit once you've built up confidence with it. I think you'll find that it's a great exercise for creating unique sounding drum fills.
Hope that helps!