What are the main principles, English language teachers have to take into consideration when they are planning the activities?

The first part is to make sure the activity you are planning is interesting and is one that your students will enjoy.
Some forms of short games always go down very well, also role plays.
You must prepare activities that all your group can participate in and help each other.
I use crosswords sometimes, however, they must be simple.
My advise is to plan around the level of your students, make the activites fun and be prepared to help your students as much as you can without providing all the answers.
Good Luck

1- Respond to children's questions and let them build thier language skills

2- Engage children in conversation throughout the day

3- when reading aloud astory to the childern, encourage them to predict what will happen in the story, to comment on the story, and to make connections between thee story aand their personal experiences

4- play games that will focus childern's attention on the importance of listening carefully

5- Gently reinforce the rules of good listening and speaking throughout the day

6- Capitalize on routine opprtunities to have the children follow or give directions

7- present new words to children to ecpand thier vocabularies

1.
level of students2.
tasks and goals3.
certain difficulties that may occur