Let’s start by defining terms. By environmental I mean factors that affect database performance outside of the code. The remediation of issues can be accomplished without altering SQL, no code change request, no release management necessary. Poor performance can often be addressed by doing a quick review of the overall system and ensuring there are not horrible defaults in use.
This is the low hanging fruit we can get before deep diving into the code
Before you start banging your head against the hood of the car take a walk around and look at the big picture first. It is a common thing to see junior DBAs go right for the most complex area they can identify and ignore the obvious issues which are plain to the eyes of a veteran DBA.
Read on for some resources to help you learn more.