For half sq triangles the Quilt In A Day triangle square up ruler is a must have. ONE cut. I always make mine larger then square up so they always come out perfect. Fons and Porter are much more time consuming to make. I have it but do not even use it.
For 2 1/2 in sqs use 2- 6 in squares right sides togather draw an x sew 1/4 one each side, cut in half both ways then on lines. Makes 8. Add two in for each size larger.