How do I gain better experience in editing English grammar?

The question seemed wide open and for this, I had to alter
it.  The first thing that one needs to grasp here is that editing skills are not
static.  Everyone needs improvement in editing.  As writers and thinkers, we catch
mistakes years later that we should have caught at the time, but simply did not.  Part
of this improvement process can be done by simply reading more and gaining great
familiarity with the language through greater reading and further exposure to language
techniques.  At the same time, there is a proliferation of grammar websites that can be
of assistance to you.  They break down the rules and give you background as to how to
construct stronger examples of grammar and further familiarity to the language, in
general.  I would also suggest that part of this process would be to identify poor uses
of grammar.  The web is filled with even more examples of poor grammar usage than
accurate ones.  I think that being able to understand the basic rules and then applying
them to the examples found online could be highly beneficial to you in your process of
gaining greater proficiency with the language.