I typically sew large and trim down which requires a variety of techniques but which I feel give me a better finished project. I keep 1/4" gridded template plastic and will make cutting templates, especially if I have a lot of blocks. Warning: Do not use the template plastic as a ruler you will cut into it or have other problems. Lay it out on the block and place your cutting ruler on the piece of fabric to be trimmed off and move the template out of the way.
In some ways easier, I also use quilters 1/4" masking tape on my rulers to show where the diagonals should be. I have a lot of rulers and keep a roll of the tape in my essential supplies.