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.