Lift knee up as he is jumping to block him (your not using your hands which he knows is a reward E.g stroking)
Once you have blocked the move you need to turn away and ignore him until he has calmed.

When your out and about its difficult if they are off the lead so ensure you ask everyone to ignore and turn if he does it to them. When he is on the lead you could always have people approach you ... put your foot on the lead up close to his collar and put him in the down position ... the weight of your body on the lead should hold him down and stops you bending down .. thus encouraging him to jump up because he thinks he is going to get a stroke (reward)
Once he is down and you have him 'pinned' down the person can approach but they MUST NOT acknowledge him until he is calm subbmissive.

Now the one thing that will annoy you is when you ask people not to let him jump up and they say "oh i dont mind..." .. Simply say "well i do, please do not let him jump up"

That used to drive me nuts, lol