Ah, these things drive me insane! I have to admit it is one area of quilting that causes me no end of grief. All those lines to draw and then stitch either side of! Argh...
Simply take two squares (I used charm squares) and sew around all four sides without removing the needle or back stitching.
Then simply cut the square diagonally from corner to corner, twice. Open and iron and you now have 4 half square triangles in next to no time and without all that dreadful ruling.