This is just an easy way when you need to cut almost all the way through wood and don't want to invest the time and money for a table saw, cutting jig, etc. I spent a bit of time trying to find a solution, and maybe you can save yourself a little time.
BTW, thing I'm making in the pictures is called kerfing. It's a part of a guitar.
Step 1: Put the Two Small C-clamps on the Saw Blade
You just want a little edge of the clamp to protrude past the teeth of the saw blade. The edges of the clamps will run into the workbench surface and stop you from cutting all the way through. It's just that simple.
Too big clamps will be too heavy and could warp the blade.
Of course the clamps can bend the blade a little and also bend the teeth, so maybe don't do this on your best saw or one with teeth that stick out to the side a lot. I did it with a cheap hacksaw blade. The small hacksaw teeth also make it pretty easy to cut through a small piece of wood without much tearing or other problems.
Step 2: Cut on a Flat, Narrow Surface
The surface has to be narrow in the direction you're cutting, since your hand will bump into the workbench if it is wider than the length of the saw blade. I'm not sure if that's clear, but you'll see what I mean if you try it.