I starch my fabric heavily and cut my squares slightly bigger so that I can
trip them to the right size. Personally, I prefer to avoid bias edges as much
as possible. If you have a lot of HST's to make there is a similar method
where you sew 8 HST's at a time.
Here it is.
http://sewmamasew.com/blog2/2013/01/...s-8-at-a-time/