Terraforming was the hardest thing for me, so I took most of my inspiration from Instagram (forest builds, lake builds, autumncore town builds). But I knew that I wanted to make a little town/village with foresty areas the deeper/farther you go into the map, so what helped me the most was starting to decorate and build around my plaza and shops first, since I had that layout in mind. Not sure if this advice will be of help to you, but I found it much easier to plan out walkways when I started with my shops.
As for interior design, that's always been the most enjoyable game activity for me. Like others have said, look up real life images of home interior design on Google/Pinterest and then try to mimic that using in-game items (it helps when you have a sense what all of the furniture in the game is) -- do this a couple of times and I guarantee it will help you become a more intuitive designer
For example, the other day I was trying to plan out my house and go for a rustic cottage type of feel. I just googled "rustic interior design" and tons of bedroom/kitchen ideas came up. You can probably recognize a lot of similar wallpaper, carpet, and furniture items just from these few images:
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