One of the best and simplest (conceptually, anyway) suggestions I've gotten when it comes to improving speed is to *not* work on speed at all -- rather, focus on holding your actions for as long as possible, and then your transitions will be quick as a consequence (because you have no alternative, but not because you concentrated on being fast).
In my experience, when people focus solely on speed, they tend to rush or overpower actions. They look off-time or imbalanced, but not particularly faster 
Hmmm...there's more to say on that, but it's time to run to a meeting so that will have to do for now!
Vaness