Many years ago I learned that if I use a piece of paper about 6" long with a nice line on it. 1/4" graph paper will work great if you keep the extra lines to the right of the needle to use the 1/4" as your seam allowance guide.
I stitch on the line, no thread in needle, for an inch or so, THEN tape the paper to the machine that is right in front of me. Then cut away the paper under the needle so you can use the line as your guide, line up the corners of what you are sewing and keep the last corner on the line as you stitch it.
I have always kept the paper taped to my machine so I can use it when needed. The paper stays taped down for years before needing to be replaced.
This is the cheapest method before they came out with other things that do the same thing but are costly compared to a small piece of paper.