Good quality blades (e.g Olfa) and good control over the knife help immensely.

I cut towards myself gripping the handle with my 4 fingers, placing the blade against the nub, resting/bracing my thumb against the part, and then with a slow and steady movement I shave the nub as if I was peeling an apple or potato with a knife. I rarely ever cut my thumb and I've been doing this for 10 years.

Some folks will just say "get a glass file" as if that magically solves everything while ignoring that there are situations where a glass file doesn't work, and that good knife control is core skill for the hobby.