Just thought I would share this tip with you since it would have saved me some of my time if I had this.
Add the following to your
.zshrc file or whatever file it is that you want,
just make sure it's loaded by Zsh:
autoload -U compinit compinit
That enables auto-completion and loads it up. I'm not sure why I never had it enabled, but now it is.
You don't really need to do anything special anywhere else I don't think, that's the only thing I had to fix for it to work on my computer.
Hope that helps. :)