I知 not very good at handcut dovetails, so take this for what it痴 worth.
First, instead of using pencil, try using a marking/cutting gauge and knife to lay out the dovetails. You値l get more precision.
Second, I tend to alternate between the chisel and a very fine knife blade as I知 clearing the material. I use the knife to score the grains I want to remove, and then remove them with the chisel.
Third, I知 meticulously precise and small with my cuts. I know some talented people can clear out pins and tails with a half-dozen cuts on each surface, but I知 probably doing 30, 40, 70 cuts with my knife and chisel to clear out the material.
As others have said, super sharp blades are critical.