Accepting an invitation
Confirm quickly and ask your host about dress code, cell phone rules and whether caddies are customary.
On the course
Keep pace, repair your marks and follow your host's lead on the format and any wagers.
Caddie gratuities are usually handled by the guest. Ask your host for the norm.
Afterwards
Offer to cover what the club allows guests to pay for. A short written note to your host is still the custom.