I use one of these.
https://www.leevalley.com/en-us/sho...ries/41780-small-parts-miter-jig?item=04K0101 or sometimes a 2 screw wood clamp of a size that will work best. For the clamp in the link, I cut some squares of sticky back 80 grit sand paper and applied it to the surfaces that hold the wood to make the clamp hold the work even better. One side of the clamp is an aluminum angle that you can ride along the fence while making the cut. It's about 1 ft long, so the clamp is quite stable when used this way. There is an adjustment for this to move it to an angle if you should want to cut the small piece at an angle, and I like the two handles that help you keep your hands high and away from the cutting area. This tool is a "must have" in my shop, and if I ever break it, I'll be ordering a replacement very soon. There are other sources for these and prices vary, so shop around. Lee Valley seems to be one of the better sources. Rockler has a blue version for the highest price that I've seen, or over double what Lee Valley wants for the yellow version, and as far as I can tell there is no difference between them, other than the color.
Charley