The single most important thing I've learned is to keep 2 fingers on the clutch and the front brake levers at all times, NOT just when I think there might be a chance of needing them. Usually, for me, excrement occurs when I least expect it.
Interestingly enough, did ya know it takes about a half second to uncurl your fingers from the grip and reach for the lever? At 60 mph that = about 66 feet. 66 feet lost when ya coulda been doing some hard braking. Personally I'd much rather stop 1 foot before the car, dog, deaf and blind senior citizen, whatever, than to stop 65 feet after hitting them.
I know, the racers don't do this on the track. I've watched them too. But I still do it on the track anyway in case some dork decides to shut the door on me when I'm half way through it already.
And, if you're riding correctly, you don't need to hold onto the grips anyway. Your body weight will be sufficient to keep your hands there... especially under braking when your weight transfers forward.