Important

If you don't read any other resources in this section, at least read through the ones linked here. 

This slideshow by Six focuses on TF2 and is a great resource on Mental Health, Communication and Morale
Mental Health, Communication, And Morale.pdf

Here is a great article on maintaining your physical and even mental well-being.
https://www.reddit.com/r/GlobalOffensive/comments/64aq95/psa_please_take_care_of_yourself_while_playing/

Here is a better formatted version, of the same content, on the cfg.tf website:
https://cfg.tf/read/health/