To get started, you really just need to understand your shutter speed, aperture, and ISO values.
But yea idk about getting a 50mm as your first upgrade; I mean I personally did get one as mine haha, but looking in retrospect I think a flash would have been a better choice for me. Both a flash and 50mm lens are viable pieces of equipment that will definitely help make you a better photographer. Ultimately when it comes down to it, it's all preference.
BTW, If you're having troube using M off rip, try to use CA, Creative Auto. That's how I first started, it's great too because it eventually teaches you how to use iso, ss, aperture.
edit-and super cosign on shooting often, i haven't been shooting for too long, but i'm still finding out new things about my camera and techniques solely due to experience lol.