I'm washi tape crazy, and if it sits still, it gets taped. I use it to decorate things like clothespins, light switch covers, ceramic tiles, paper mache boxes, as well as paper projects like cards and tags.
I like using assorted colors of painted backgrounds to change the way the tape appears. Try using several colors with the same tape to see varying effects. For example, with my clothespins I ordinarily paint them white before applying tape, but I've also made sets with, say, three pastel colors and applied the same tape. The result is novel because the tape is translucent (most of it.) Here are two sets I made that show what I mean. Each set is decorated with the same tape but the clothespins are painted different colors first.
You have to be careful with knock off tapes because they don't all have the same adhesive qualities. Some will have very little stickiness, some will stick too much and not be repositionable. For most of my projects, I will seal the tape with decoupage glue and/or acrylic sealer, because it will eventually peel off. At the same time, that is one of its redeeming qualities. You can remove it without leaving tape residue. I decorated a mason jar for 4th of July, then removed the tape and reused the jar for another project.
Here's my American flag---an idea I got from another blog, "Washi Tape Crafts."
Most washi tape is sold online, and the prices range from $2.50 - $5.00 USD per roll, depending on if it is true designer tape from Japan or a knock-off from China. Also, don't confuse Korean "Deco-tape" which is plastic, not paper. Some scrapbooking companies are making tape for sale in stores, like K&Co. Because I like to make things that are coordinated, I've been using a lot of the Scotch brand that came out recently. It's available at many office supply stores. Online, Cute Tape has a fine selection and good prices. Here's most of the tape I have. None of my Christmas tapes are included.