If you really want to gain knowledge and confidence in the fundamentals, spend some time watching (in real time, NOT sped up) an excellent artist. Good art is often very slow. I saw a huge improvement in my own (self-taught, hobby-level) art when I began to get comfortable spending 10 hours on a drawing instead of one. I enjoy drawing portraits and can recommend this guy's Patreon: https://www.patreon.com/stephenbaumanartwork