tmux is an awesome tool. I will try to get some of my bookmarked resources collected here. To begin with a nifty cheatsheet from Reddit or another cheatsheet.
I found this great article on how to customize the tmux status bar.
And then there is of course always the man page.
The tmux plugin manager (tpm) is a necessity. It is installed by cloning the repository. See the TIL entry on Use Tmux Plugin Manager.
In can recommend tmux-sensible and resurrect (see: Use Tmux Resurrect).