The inductive approach focuses on providing evidence from which you derive a conclusion. It is full of hypotheses and "hopeful" conclusions, but you cannot prove your conclusion beyond doubt. When this is applied to teaching English grammar, it means that you provide your students with a lot of specific examples (i.e., spelling/grammar rules, parts of speech, sentence structure types, etc.). Afterwards, you explain to them that they can use that evidence to come to a conclusion about how they should write or say something, but that their conclusion will not always be right (because of the many exceptions in the English language).
Deductive reasoning, on the other hand, begins with a generally accepted truth, such as "English grammar is difficult to master and has many different nuances because of the contributions of so many other languages. From that point, your students will know that this is the type of grammar with which they'll be working, and then you provide rules/suggestions for various situations and teach them how to apply those rules/suggestions for grammar in very specific scenarios or contexts.