To decorate your office for Valentine's Day, start by choosing a theme, such as hearts and roses, cupid-inspired art, or bright reds and pinks. Next, consider the decorations you wish to craft. For instance, make large paper flowers using cardboard or foam cores lying around the office. Or create a festive banner using felt lettering on long pieces of ribbon, spelling words like Happy Valentine's or Be Mine. Additionally, fill large helium balloons with romantic messages using permanent markers to create conversation starters. For extra flair, add colorful streamers to the walls.