I'm using Triangles on a Roll paper, my favorite method for HSTs. Here's the paper pinned to the fabrics. I pin it to the lighter fabric so when I press, I can press the seam allowances toward the darker fabric.
Here's a close-up of the instructions:
For 12 blocks I made 48 triangles. Here they are cut apart:
Nest step: tearing off the paper and trimming the ears:
Striped fabrics end up vertical and horizontal, but when you move the HSTs around they work: