There are a lot of ways to go about creating a themed office, and it all depends on what you want your theme to be. For example, if you wish to a movie-themed office, you can print out movie posters and hang them everywhere or have workers bring their movie posters. Or you could recreate various movie scenes in each cubicle. How in-depth and expensive you want to go with this is up to you.
The number of these ideas is endless, and you have to find what appeals to you and other office workers if there are any others. If you are designing an office for multiple people, find something that everyone can collaborate on and contribute to save costs and keep everyone vested and involved in the changes.
Offices don’t have to look formal. They can be quite the opposite and seem like someplace that is lived in. You can make your office space more comfortable by giving your employees or yourself some freedom to bring in items that make it feel like home. Set up family pictures on your desk or your wall, bring in a few things from your favorite hobby and personalize the office as much as you can.