That Steve Sells video is pretty much all anyone needs to START off with, and then let each gun's uniqueness tell you what IT wants, along with YOUR preferred method or style loading.
"Flint lock tuning" can be different things. Initially it's about getting a proper sharp flint and positioning it well in the cock jaws with respect to where it addresses the hammer steel and where it winds up facing the pan. There are two types of lock fints - common (thick and double edged) and fine (thin and single edged). I vastly prefer fine flints and you can specifically ask for them at TOTW in either english or french versions.
Getting consistent and fast flint ignition is perhaps the prime bugaboo of most flintlock pilgrims, and even for some old timers, and there are a myriad of reasons why, with loading process neglects probably most common. Humid weather can be a big issue in the world of no flint lock ignition, too. Last Summer a humid day at the range got me fits for keeping the pan, frizzen face, and flint edge dry and clean until I switched from Swiss 3F to the Swiss 1-1/2F coarser powder that I use for BPCR cartridges, and that helped a heap. Ignition was still purty fast, too. Coarser kernals of powder won't sop up humidity as much as the much finer pan powder will. I might eventually wind up with Swiss 1-1/2F as the only powder I'll need for both muzzy and BPCR guns. Works for me if it works well!