When I started getting serious about digital art, I got involved with a number of art contests on ArtStation, Mythical Beast Wars and CG Hub.
The communities on these sites were amazing, filled with people willing to provide guidance, paint-overs and encouragement every step of the way.
In time, I was giving advice as well as receiving it, an experience which taught me a great deal about how to give meaningful criticism- and how to accept it gracefully.