I've tried a variety of methods for sewing this type of triangle and I'm always unhappy with the result. I finally decided to just be old-fashioned and lightly draw a pencil line from corner to corner and follow it as my stitching line. I get much more accurate results than pressing in the stitch line or just eyeballing it. I try to organize the process by cutting all the squares needed, then doing the stitch line drawing during "hand work" time (usually while watching football on the weekends!).
When it's time to stitch, I just line everything up and chain piece one block after another.
After stitching, I use the trusty rotary cutter and ruler to trim off the excess triangles and leave a quarter inch seam. I don't like to throw away the sliced off triangles, so I immediately scoop them up and chain piece them through the machine as well. I find if I stitch them into half-square triangles immediately, I'm less likely to get discouraged by their size and number and wind up tossing them in the trash.
In this case, I'm just using a quarter-inch seam guide (the magnet on the sewing machine bed), as I don't particularly like that 1/4 inch presser foot and I was too lazy to go get a better one from another machine! When I'm finished chain-stitching these, I leave the thread attached and just save them for another project.
Another method for "saving" the excess triangles would be to use the diagonal line on the corner squares as a presser foot guide. Make two parallel rows of stitching on either side of the pencil line, then cut the squares in half diagonally along the pencil line. The result is the corner triangle on your pieced block and an extra set of half-square triangles for another project!
