Principles
You cannot teach all of English. You cannot teach all of English grammar.
The Longman Grammar of Spoken and Written English has 1203 pages and the Cambridge Grammar of English has 984 pages of exhaustive analysis of the English language.
No teacher can master all of this or teach it. Nor do they need to try. These are reference grammars not pedagogical grammars.
Coursebook Grammars
Coursebook grammars are the closest we have to pedagogical grammars but they often have the serious problems which we discussed in The Grammar Problem.
In the 21st Century we need a new approach to pedagogical grammars, one which reflects our understanding of the language thanks to corpus linguistics research and one which recognises that most English language teachers share their learners L1.
Now is the time for a re-imagining of English grammar.
Principles of Pedagogical Grammars
A pedagogical grammar should be designed to help the learners learn the most important grammar ideas and most powerful conventions of the language.
Once the learner has done this then they can then set about learning the rest of the language which they think is important to them.
While they are doing this a dictionary will be more useful than a grammar.