Some noobs out there have horrible videos on how to be good at spy, and believe me. I've watched them all. They SUCK. Here's the ONLY working guide that will help you reach success as a decent spy. Not GREAT, but decent enough so that your teammates won't keep shouting at you like they did when you played DotA 2 two months ago. (You quit.)

Coolrock 43's Channel: https://www.youtube.com/channel/UCYwPdXQhc47uBUPMnQ_8eHQ

https://youtu.be/6BmNQYXCzyo