I travel solo, but always request a table for at least 8, prefer 10.
This way you know you will have conversation at dinner, I work my way round the table, so no one get "stuck" with me (or other way around) every night.
At breakfast and lunch , I always ask to be seated "at a large table" that way I meet people . Have I ever had trouble with other passengers, yes , but that is their problem not mine, I am prepared to smile and be friendly with everyone.
On two differnt cruises with two different line, both with less than 400 passengers I did find myself "refused". and ended up sitting at a table for one. Never cruised with either line again. Reallised I had made a poor choice, too few passengers, many acted as though the ship was their private domain, and many were from rather "specialised clubs" . I was regarded as interloper.
Research the LIFESTYLE of the ship,(do not choose dressy if you prefer casual,or a party ship if you want a very quiet cruise) the number of passengers, and if possible the activities you will wish to do.
Regardless have a wonderful cruise.