I'm not so sure about ukes because i'm new with them but I'll share the maintenance that I do for my acoustic guitars.. I don't think they'll be that different.
Things I look out for that help:
1) Changing strings... especially if you use it a lot. I think changing once a year is a little too long to wait to change strings especially with heavy use.
2) Wiping the strings and fretboard after playing.
3) Washing hands before playing -- lotion, sweat, etc. can accumulate on your guitar (including the strings) that can dull them and affect sound quality.
4) When changing strings, I use Fret Ease (it's a bottle spray I get from guitar stores) and wipe it on the fretboard. It can be also used to the strings and fretboard even you are not changing strings. Only thing is, is before I use it the first time on my guitar, I make sure that it won't damage the finish. So far it's safe with rosewood fretboard. You can check with Kamaka if what's safe to use on the fretboard to recondition it. Dirt tends to accumulate on the fretboard and strings which can affect the sound.
I hope it helps! :shaka: