It depends on 'why' you're standing.
If you're on a long climb and standing to change up the muscle load a bit and get some rest without losing too much speed you just gently rock the bike back and forth and let your body weight fall on each pedal. In this case the upper body is fairly relaxed and just rhythmically swaying the bike from side to side.
If you're standing to deal with a particularly steep grade then you actively pull on the bars and really claw at the pedals to deliver the high torque needed to climb really steep grades when you lack the low gearing.
Pretty much the same thing but more dynamic if you stand up to attack or close a gap, pull more on the bars, use a lot of force on the pedals, perhaps focus on pulling up a bit but still most of the power comes on the downstroke
And if full out sprinting it's similar but you'll be more crouched, not standing tall or extending your legs fully on each stroke, keeping your arms heavily flexed both to allow a firm pull on the bars and to hold a low aero position as you accelerate in a sprint.
They're all versions of standing up but they're all a bit different.
-Dave