My preferred method of making HSTs is to start with squares. If I want a 2" finish, I cut 2 1/2" squares. Sew two squares together on the diagonal, trim away the excess, press open. Perfect HST. However, there is a lot of wasted fabric. I could sew the cutoff triangles together, but rarely do.
I made lots of HSTs for my ugly fabric challenge and I didn't have enough of many fabrics to waste. So I tried a very cool ruler designed by Rachel Cross for Creative Grids (my favorite brand of ruler).
You can use one side of this ruler to cut 2 1/2" strips, or do it with another ruler, which is what I did. Because I wanted to work faster, I stacked 6 strips. I paired my strips right sides together so that they were already matched for sewing. FYI – I prewashed and dried my fabric so the triangles stayed stuck together well.

It helps to place the strip stack near a corner of your table (lower right in my photo).

Square off the left side of the strips.

And the right side. The strips need to be the length of the ruler, or shorter. If your strips are shorter, the left end needs to line up with the long side of one of the triangles, as I show in the next photo.

Hold the ruler firmly, keep your fingers out of the way, and cut carefully. If you have stacked strips as I did, be very sure you keep your ruler straight. If you angle it as you cut, triangle sizes will vary.

Being at the corner of your table allows you to hold and cut in the other direction more easily.

Work your way down the ruler.

Separate the stacks of triangles, turn half of them so that you can line up the flat sides as shown. The very pointy edges are away from the ruler.

Carefully place the ruler over the stacks and trim off these dogears.

My Bernina has a little 1/4" mark in front of the feed dogs. I always rely on this mark when piecing. It, together with the edge of my 1/4" foot, help me to sew accurately.

Control the fabric as you sew.

Even though I sewed carefully, there were still some minor differences in size when I pressed them open. I trimmed some that seemed to really need it but for the rest, I worked with what I had, making minor adjustments as I sewed. Nearly all of my points matched perfectly – yay!
I would use this ruler again. It's fast and there isn't waste. For other quilts, or when I need a different size HST, I would probably start with squares as I have in the past. But it's nice to have one more way to make them! If you are interested in one of these rulers, I have them online here.