I had problems with HST and tried many methods even the fabric sheets preprinted with the lines to sew.
But I finally found the method for me. It is the Quilt in a Day way.
If you get the triangle square up ruler it has all the sizes and the square up lines that you only have to cut one time to square up. It is fast and easy with just a scant of fabric to cut off. Mainly you get perfect HST and you get 8 at a time.
Try it out for 2 1/2 inch Hst. Cut out 2 six inch squares and place them right sides togather. Then draw and x and sew 1/4 inch on each side of lines. Cut the square in half on both sides + . Keep the square togather and cut on the drawn lines. You will have 8 - 2 1/2 triangles. You can square up as usual but with the ruler you only make one cut. The ruler is place just above the stitch line and lined up on one side then you cut off the one edge and you can cut the tails at the same time. Press and you are done. 8 at a time and all perfect.
http://quiltinaday.com