Remember to change the needles, too.
A jean-a--ma-jig -or similar gadget/device/tool - also helps.
I use a longer stitch - at least a 3 or 3.5 - when hemming jeans.
Also - if the jeans are tapered, releasing the the seams below the fold lines sometimes helps get a smoother, unpuckered, hem.
If working with extra heavy jeans, and the flat felled seam is like triple stitched, I will clip to the first fold line, and let that amount stick up above the stitching line. I usually trim it even with the fold line and put something like fray check on the raw edge.