I have a small spare room that I'd like to turn into a home office. It's a blank slate. Where do I begin?
Let's begin with the room scheme and colour palette. Is the room to be modern, traditional, all-business, a man cave? And what colour puts you in a working mood? Try to keep to a palette of three colours maximum so that they don't distract you.
When you say the room is small, I would guess that it's windowless, in which case adorn the walls with panel moulding and add a mirror or wallpaper for big impact. You'll need good lighting – try a desk lamp with plenty of style and make sure that your overhead light isn't aimed at your back when you're at the desk because it will cast shadows over your work. If space permits, don't put the desk against the wall.
Try to have it open to the room with a love seat facing it. Many of us work better on a sofa than at a desk, so consider eliminating the desk altogether and creating an office lounge: sectional sofa, area carpet, floor lamps, appropriate plugs for devices, even a coffee table for your latte.