I'll add do all the activities they offer, there are very few cruises that will be similar and less likely to go a second or more time. People on my boat missed an amazing sunset at a rookery because they were too busy drinking and chatting one night.
Get a physical if needed to get sign off for doing a polar plunge.
Go to all the talks, or watch on your room's tv if offered, the staff are passionate and knowledgeable.
You're already going to be in Argentina/Chile most likely, hopefully have time to see more of those countries.
Avoid penguin poop at all costs, it's oily because of their diet and smells horrible. Will sit in your clothes for a while. At least it's very easy to spot.