What is the easy way to teach Tenses in English Language at school level?

First intriduce your students to the list of tenses. Take one tense daily, explain its rule and try to teach them with the help of simple sentences. Use same sentences for all the tenses. 

Give more sentences to the students to have more practice.

Revision is must to keep it in mind.

You need to draw a map of the tenses then tell them which tense they will learn. There are12 tenses in English, however the most used ones are few. Establish general concepts of forming sentences such as using auxiliaries, making negative forms, etc. Then teach the tense you want in two levels:

1. The form

2. The use

In the form you have to stop at three points:

The form:

A. Positive (or affirmative) sentences.

B. Negative sentences.

C. Questions (or intorregative sentences):

   i. Yes/No questions (or short answers' question)

   ii. Wh questions (or long answers' questions)

You need to give clear examples and classify the pronouns in groups (when required) and do not forget to tell them when and why we use that tense because each tense has its own use(s).

I hope that will help