Lighting!! Lighting dramatically effects any work space, or really any space at all for that matter! Ever notice how on rainy/cloudy days you don't really like to do much of anything but cuddle and sleep? That's the general idea! When things are bright, you automatically wake up and start the day on an energetic note. You will notice that with proper lighting, you'll start enjoying being in your office. This isn't a DIY however, you'll need to hire a good Los Angeles remodeling company because they will know the best in the industry. You don't want to just hire someone out of nowhere or solely based on reviews online.
You don't need giant, bulky, grey metal filing cabinets to bring you down. Opt instead for a dual filing cabinet with a sleek design; that way it's not taking up unnecessary space and it looks good. Look for furnishing items like this, try to keep everything organized and out of the way because clutter is very distracting and it's ugly too. You probably need shelves to but you don't have to get the whole case, instead get built-in bookshelves. This once again, saves space, looks good, and is just as, if not more, efficient.
When it comes to furniture you should definitely keep in mind the size of your office and how big your desk should really be. You don't want it taking up so much space that you don't need because more clutter means more stress.