SOP dependent...
1 Speak to ground crew and make sure everything's ready
2 Get pushback clearance from tower
3 Beacon on
4 Finish the checklist
5 Push
If the beacon goes on before you've spoken to the ground crew then some are trained to move clear of the aircraft, which isn't particularly useful if he's half way through doing the final walkround.
If you ask for pushback before speaking to the ground crew this can be EXTREMELY frustrating for aircraft around you if you go to talk to him and he's not actually there and you're in a situation where only one can push back at a time.
Anyway, horses for courses really...