I have a couple different "neighborhoods", but also some houses that are in their own area. I focus on villager aesthetic/personality when I figure out where to put them.
For instance, here are two of my neighborhoods:
The left one is the "main" neighborhood (though it just has two houses, currently Chevre and Julian who happen to match perfectly) and it's just to the right of my RS plaza. This was the first proper neighborhood I ever started making, Tammy has her house around where Chevre's was on the first day! The beach neighborhood (the two villager houses pictured, and one of my character's houses off to the right) on the right is just below the main one (the wood path you see at the bottom of that pic leads to it).
In my orchard pic you can see the start of my forest behind it, and in the top right corner, you catch a glimpse of Erik's house. Since he's a reindeer (side note- I made his catchphrase "reindurr" and it makes me laugh more than it should) with a cabin I thought it fit nicely in the forest.
I also (though I don't have pictures) have a "fancier" neighborhood on the western side of my island, with some flowerbeds and larger yards. Cleo, who lives there, even has a pool! Again, it just has two (Merry and Cleo right now).
I've also got Dobie's house on a tiny scrap of beach that's mainly private (I put one of the shabby bridges leading to it, so it looks super secluded). I like his house there because he's a cranky old man, and it would allow him to yell "Get off my lawn(beach)!" all he wants
Like Erik, Freya lives in the forest. Her house is on a hill, with some wind turbines by it. It looks very pretty and for some reason gives me a Scandinavian vibe there, so I think it fits.
I frequently move houses when new islanders come in, too, so their houses are in JUST the right spot. Since you can move houses as much as you want (for a fee, of course) it really helps with island planning, since you don't need to worry about a spot being good for one villager, but seem ridiculous for the next!