I started studying Koine Greek independently in 2013. My views on the Greek language are conservative. Everything I believe about the Greek language can be found in standard beginner and intermediate Greek textbooks, such as those I recommend below.
About 50 years ago, Frank Stagg wrote an influential paper called The Abused Aorist. This paper has helped many people avoid common mistakes with the aorist, such as viewing every instance of the aorist as conveying "once-and-for-all" action.
In the spirit of Frank Stagg's work, I have written a few articles that expose what I believe is an abuse of the Greek present tense. In particular, I am quite critical of an increasing number of interpreters who incorporate their theological bias into the present tense. It is a serious abuse of the Greek language that I think it is just as significant as the abuse of the aorist.
Essentials of New Testament Greek by Ray Summers
Learn to Read New Testament Greek by David Alan Black
A Greek Grammar For Colleges by Herbert Weir Smyth
The Basics of New Testament Greek Syntax by Daniel Wallace
The Greek Testament Commentary by Henry Alford
Word Pictures in the New Testament by A.T. Robertson