My Mayor's house is just all over the place, really. I have one fancypants regal/rococo room, one that's full of candy and sweets, one that's stuffed with rainbowy-pinky stuff, one housing my princess set, a flower/garden room and the basement is, for the moment, still just storage. But what usually helps is I'll find an item or two that I adore, and decide "this NEEDS to be in my house - how do I complement it?" and then I "build" based around that item, or whatever.
With my side-characters (who are not-so-secretly pattern/storage mules, shhhh don't tell them!), they're ports of D&D characters I've built but never had the chance to fully realize or just loved too much to let go. In both their cases, it's much easier to figure out what I want their homes to look like, and what to do with certain rooms.
One is a fairly eccentric doctor with a love of all things cute, for example, and due to backstory and things that happened during his campaign, it was established that he came from a poorer area and ran a not-so-legal clinic. Also, super into eldritch gods. So I think - what would he do with all that space, if he finally had it? He'd carry on with his practice, so that's one room for his hospital-y stuff, TWO rooms if the main one is treated as a separate waiting/reception area. Then he'll have his standard kitchen and bathroom. The bedroom will be where all his cute stuff goes, and the basement is going to be where all his freaky **** goes. Makes sense for his character, even though it's probably weird someone out if they were just passing through and decided to check out his house (once I finish it... T_T)
Second is a lass who's worked as part of a merchant caravan (alongside khajiit characters, in the game she came from

) so I draw from typical merchant stuff - there'll be rooms full of vases and antiques and the like. Then there'll be a place for seedier activities like gambling. Maybe a place where she'll display her own collection of instruments and swords and other stuff she's taken a liking to. Not sure what to do with her decor yet, since there's a lack of distinctly indian/arabian/etc influenced stuff up in this game, so I imagine I'll spend the most time sorting out how to organize all her stuff.
Once I have a general idea to work with, I pile ALL THE FURNITURE into the room. Like, just shove it all into a corner. And then I start pulling things out to where I think they might look good... it all goes from there.
...hey, you asked.