There are several methods for making HSTs. Quilt in a Day has a Triangle Square Up ruler that I like, because you square the HSTs after you cut but before you press open, so you only have to trim 2 sides. June Tailor also has a Shape Cut type tool for marking, cutting and trimming HSTs. Then there are Thangles or Triangulations or a product that is on roll, where you cut and layer fabric strips, then sew using marked paper strips. The finished HSTs are usually very nice, there's no trimming, but you have to tear the paper away.