Slowly and carefully (I think) are the first two rules for shaving under the nose. I started with SR when I still had a goatee for the winter. I got to cheat by "practicing" on the large flat areas and learning how my razor acts. After a few months, and warmer weather, I shaved my full face. Still had to be careful.

There is lots of good suggestions here. It just becomes trial and (hopefully not much) error to find what will work best for you.

I would hold the opinion the "pulling" your nose to one side or the other, out of the way, is a good idea for most any method.

Enjoy learning