Since August, I have been on 3 short P&O cruises, 3 shortish Princess cruises, a 4 day Royal, and a 7 night Carnival cruise. These all had the mask requirement onboard and I did
not get covid.
3 weeks ago, I went on an 8 night Ovation and tested positive on disembark day. No masking requirement onboard but I wore my N95 ( one of the few who did).
I agree with all the tips the above posters have provided and practiced those myself. I avoided certain activities that I normally enjoy e.g fitness classes but still got it. I think it's likely I picked it up at one of the crowded music trivia sessions where it turns into a loud sing-along......all those covid particles floating around 🙂
Be careful, assess crowded situations but still have fun!