If you have never been on a cruise before, the idea can be quite scary. All alone at sea with no way off can inspire nightmares among the uninitiated. The first tip to give someone who has never been cruising before is for them to understand that a cruise ship is like a large city. There will always be plenty to do and plenty of people around, so you don't have to feel isolated or alone. And cruises have learnt from the mistake of the Titanic and other sea fearing movies. They all have plenty of life boats and safety instructions so you will be given plenty of notice should the unthinkable happen.
In your own town you will generally gravitate towards what you know, and that will be the same on a cruise ship. However, don't just limit yourself to what you know; be adventurous and try new things. Many cruises offer dance lessons, be brave and sign up. Some will also have karaoke nights, so show your voice to the world, or at least the small section that are on the cruise. You won't know about these things if you don't look them up, so get a detailed itinerary of the ship before you go and make a note of everything that sounds interesting.
It will also pay off to take a long walk around the ship as soon as you get on so you can get a feel of where everything is, as well was work out the best way to get to the dining room for dinner.