A bit older, but still a very relevant blog post about the vision behind Substrate.

In this video tutorial, Bill Laboon walks you through the process of choosing validators to nominate. Note that most of the information can also be applied to Kusama, Edgeware, & HydraDX

Florian Liss, Technical Lead at Staking Facilities, talks about the ins & outs of Nominated Proof-of-Stake.