You're going on your vacation; so be sure to wear whatever makes you feel most comfortable! The day to day life on cruise ships and at ports very casual and relaxed. It goes without saying, but warmer climates imply more lightweight clothing and fabrics and for colder regions you be will well equipped with whatever makes you feel warm and comfortable.
For footwear, again, it depends the destination and climate. But a good general advice is to bring comfortable walking shoes, and maybe a good pair of sandals for shore trips.
It's also always a good idea to bring something for rainy days. So a waterproof hat, an umbrella or a raincoat are always a good thing to have.
Evening dress codes are different from ship to ship. As you might imagine, the code on a large cruise liner will be quite different from an almost yacht-like experience. The majority of ships offer many different restaurants, for which the dress code will go from casual to smart casual and formal. The recommended dress code on the ship's main dining venues consists normally of casual shirts and slacks for men, and sundresses or pants for women, but lots of people prefer dressing up, and that's fine!
Blazers, suits and ties for men, and cocktail dresses for women are recommended in more specialty restaurants, and on luxury ships.
A black suit for men is more than sufficient during formal nights, as tuxedos are not the norm anymore.
All these dress codes are however suggestive. Always go with what you're most comfortable with!