Remove shoes before stepping into the boat. Make sure feet are clean. Do not sit on the inboard engine cover. When docking, offer to grab a rope and be prepared to jump out and tie up. Offer to pay gas money.
Boats often cost a lot to maintain.
Like it or not, a boat owner often asks people to go along just so they can do some skiing themselves. When you return to shore, offer to stick around and help clean up, tidy, wash, and trailer the boat. The worst part of the day is definitely at the end when it's time to clean up. The content following each tag should be no longer than 200 characters. Make sure the last tag includes a tag.