If you're a "tanner" days at sea will be a bathing suit. In port casual and prolly a suit underneath depending on what you're doing that day. Evenings, after dinner, it's a pretty casual scene, meaning jeans and a nice top.
during the day its shorts, t-shirts, tanks, or bathing suits.
for evenings - the dress code for the evening will be written in your ships daily paper. Shorts are not allowed in the main dining rooms during dinner, and most lines do not allow jeans in the main dining rooms.
For casual nights dress like you would if you were going out to dinner at a nice local restaurant back home. Dockers/polo type shirts are the basic "uniform" for men. Ladies- sundress, sheathdress, nice trousers/blouse, casual skirt/nice blouse.
For formal nights - go all out. Tux if you choose, or a dark suit or suit separates for the men. Ladies - long gown, dressy long skirt w/dressy or sparkly top, dressy cocktail dress, dressy suit, dressy pants w/dressy or sparkly top.