Absolutely stand up for a sprint. If anyone is interested, here's kind of how I do it. Not an expert, but getting progressively better:
Before the sprint, get in your 'sprinting gear' - as Andy said, best to target something where you'll stay around 120 rpm as long as you can - stay seated and put your hands on the drops. Last pedal stroke before dropping the hammer: get off the saddle and move your butt behind it, extend your arms, and lower your centre of gravity (same position as when you're braking downhill). Sprint, all at the same time: Move your body forward and up to maximise the punch, grip the drops and basically treat them like a barbell that you're trying to get off the ground (pull like it was a deadlift). Once you get up to the target cadence, ideally, you would simultaneously pull with your arms wile pushing down on the pedals.
You're looking to improve your sprinting,
@berty bassett?