I follow the procedure on the can.
IIRC, the thumbnail version would be:
1 Engine running, AC on MAX
2 Connect charging apparatus to top of can, with puncture/close valve retracted
3 Connect filler doo-dad to LOW pressure port
4 Screw puncture apparatus down, then reverse to allow refrigerant into system
5 Fill until indicator arrow is in the green area of the gauge
6 Close valve, remove filler apparatus from AC system
7 Replace protective cap on low pressure port