1. Dress your cutie in red or pink, and have them stand against a plain wall or solid color curtains. I happen to have pink walls in our dining room, which was perfect for Spork. Tater was wearing pink, so I had her stand in front of a wood door. She decided she needed pearls and 3 headbands, so I went with it. Take a close-up photo, and make 4x6 prints.
2. Cut around a self-adhesive mustache, so the adhesive backing is still in place. Attach to the upper lip with a piece of double-stick tape. Tater's pink/red felt mustaches were from Target. Spork's furry black 'stashes were from Dollar Tree (and didn't require cutting as they were individually backed - woohoo!).
3. Type up "I mustache you to be my friend/valentine!" Cut with a large paper punch or in comic book style strips, and attach with double-stick tape.