My home office is designed to help me focus, but also to satisfy my wandering mind.
I can't stress how much having plants in my office has improved my general mood. I have a dieffenbachia, a sansevieria, and two ZZ plants in my office, all great in low light and hard to kill.
It's pretty great to have a whiteboard in my home office. It helps me keep track of the things that float out of my head during the workweek. I also use notebooks like crazy for this!
I've also found that having my Bass in my office is a great way to take a break from writing (words or code). The same goes for having some books in my office. I keep about a fourth of my home library in my office (a few dozen are on the floor and need some shelving).
I have a second desk (previously my gaming desk) that my brother will sometimes use when we pair program on stuff. Generally, though, I prefer others don't come in my office, so it remains a space focused on work for me. My wife (who works from home too) tends to keep to her office (down the hall) or one of the other rooms in our house while I work.
Also, I'm a big fan of candles/scent diffusers, but sometimes I have to ventilate the room when I overuse them.
Unfortunately, I haven't done a great job of decorating the walls in my office and I think that would have a pretty positive impact on my mood. That and adding some ambient lighting are the next two things on my wishlist.
Other things I wish my home office had: better wall colors, more windows (stuck with one at the moment), and sit/stand desk (missing this from my old office job).
My desks, some books, and the walls:
My Bass and some of the plants:
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