Reddit mentions of Vector Basic Training: A Systematic Creative Process for Building Precision Vector Artwork

If you don't mind spending a little money, you might look at this. He assumes that you have Adobe Illustrator, but much of the material is good even if you don't. https://www.amazon.com/Vector-Basic-Training-Systematic-Precision-ebook/dp/B015NEX6L2/

The two big takeaways from the book are (1) placing the anchor points at natural extrema with handles that are parallel and perpendicular to each other (usually, but not always, horizontal and vertical) and (2) simplifying your workflow by using the addition/subtraction of shapes to create commonly used pieces.

Edit: If what you want to do is create really good custom lettering using the pen tool, you might look at Jessica Hische. I've seen her do a video (sorry, can't remember where) that covers the placement of anchor points and handles in lettering well. And for lettering, creating composite shapes for reuse (the other strong point in the book I cited) probably won't be relevant.