I just love this triangle washi tape from the Matinee add on! Here's what I did to make trimming triangles from the washi super easy...
I first applied it to cardstock, trimmed the cardstock along the washi edges (so that I ended up with a nice sturdy strip) and then cut the washi into triangular pieces. Then rearranged the pieces and attached them into place along the card base.
Finished the card off with a "hello" veneer bubble (Popcorn add on) and a few enamal dots (Front Row Card Kit).