Easy personalised letters
Washi tape is my new best friend
Then really just stick your washi tape in what ever pattern or colour combination you want.
Pick which side is going to be the back of your letter and make sure all your tape joins are on the same side.
You can experiment with vertical/horizontal or random lines. I found that on some letter like the Z is was really hard to do the edges so I made a pattern on the front and then ran new strands of washi tape all the way around the edge to cover all the messy overhang. Alternatively you could leave the edges tape free.