Looking to get serious

I started playing wow in summer of last year. I had to stop till about a week ago for personal reasons. While I played I was more of the casual player and I was dumb and spent money to fast level toons to 120 just to be able to play them. I never took the time to really learn the class or to learn any dungeons,raids, and mythics. So now that I am back ( about a week now) Im looking for like a mentor to help me learn the game better. Everything from playing the class right to add on’s and what not. I want to build up from the casual player to some one that can do everything in the game. I have fully committed my self to just playing wow for now. So if there is any one out there that would like to show me how to play the right way that would be great. I have no problem starting a new character fresh. I mainly was playing mage a warlock but I am open to learning a different class. Right now I am on the Arthas realm but will make a new toon on what ever. Thanks in advance. And if it matters I am a grown mature adult so no worries of being the kid that dosent listen and what not. I know that is a thing with people playing games now. Thanks again.