Well I've finally hit 1000 hours on spy in Tf2 and I just wanna thank @Pulsedog for being a good friend and helping me out with lewena and HLAE to get the 3D view I guess you could call it. So yeah again I hope you enjoyed :D
What @noluckman said is right it’s really no easy way to get better at spy apart from playing the game and playing spy the way you like but one way I started out was watching slurgi
I'd recommend watching circle strafe stab theory by ezra or the much more lengthy but overall better one by culruldud who originally dropped this knowledge bomb. Circle strafe theory along with other techniques like c2c will give you the tools and knowledge but not the execution. The execution part is a lot of grinding without ever realizing that you got better through it until you look back. Anyways, you still need to put in an ungodly amount of hours.