I am first going to decorate a straight-edge mug like this one. Simply wrap the washi tape of your choice around the cup, lining it up along the top edge. Although not absolutely necessary, I prefer to leave approximately one inch at the top of the mug clear of any tape or Mod Podge. This is so you mouth does not come in contact with the tape or Mod Podge when drinking.
Using your X-Acto knife, carefully trim the tape at the handle.
Press down on the tape firmly so it is secure.
Add some additional tape at the bottom. Get creative. Use several different colors or patterns.
For a slanted-edge cup, the technique is a bit different. This image depicts the WRONG way of placing the washi tape on the mug. Because of the slant of the mug this tape will not be straight and/or bunch and wrinkle.
To create straight lines on a slanted mug cut small 1" strips of washi tape. Lay those pieces down one at a time and adjust as you go around the mug, keeping the line straight.
Don't worry about seeing the spots where the tape overlaps. You can always cover that up with vertical strips of tape.
If you like you can apply vertical stripes to you mug.
Again, get creative! Mix and match, you can even create a quilt-like pattern with your tape.
Next apply the Mod Podge to the cup using your sponge brush and a work surface or plate. Make sure you are using crafting Mod Podge that is dishwasher safe. Cover the entire mug with an even layer.
Allow the Mod Podge to dry for at least 30 minutes (or overnight) and apply a second coat. This will securely seal the tape and the mug.
All done! Wasn't that easy? These would make for great custom holiday gifts as well as Mother's and Father's Day mugs :) NOTE - since this was published we washed one of these mugs in the dishwasher. We did notice some peeling of the washi tape. I recommend hand washing.