I strongly suggest you use a kitchen scale and weigh your ingredients; especially the flour. Use measuring cups or scoops the first time, weigh what you got. Next time just use the scales and make whatever adjustments based on how they turned out last time. "Two and a half cups of flour" can vary quite a bit from one batch to the next.
Grandma was probably practiced enough to adjust the lard and milk on the fly (and not even know she was doing it); you're not and probably never will be, no offense. The precise amounts of salt and baking powder are not critical, you just have to be close with those.
I used to have a knack for making biscuits, and I lost it by not baking them for a few years. And I don't cook them often enough to get it back. Frozen biscuits are so good now, it's annoying