The first reason I chose these 3 points is because I think that doing one of them (or all of them) can ruin your lesson completely. The second reason is because I see teachers doing these things all the time. Alright, here they are!
You might ask what useless things are. In my opinion, a useless thing is any kind of stupid grammar exercise such as fill in the blanks. Not all fill in the blanks exercises are useless, but those where the ESL learners have to put the verbs from the brackets in Past Tense for example. They have the verbs, they have the list of irregular verbs and all they have to do is to copy the past tense form of the verb from the list and write it in the blank. This activity is time consumption and so unproductive.
If you really want to do a fill in the blanks activity then you can ask students to choose the appropriate verb from a list of verbs. At least in this kind of activity they have to understand the meaning of the verbs and the meaning of the sentence they put the verb in.
Another completely useless thing is to do nothing. It happened to me many times to finish the lesson earlier than I planned and have extra 5-10 minutes. I believe this is a precious time to review something or play a game.
Many tasks that required individual work or different extra reading activities are completed in the class. They should be done at home as homework.
It’s your duty as a teacher to know your students level and use appropriate vocabulary when speaking to them. You might think that they will learn new vocabulary if you use it, but is not like that.
The truth is that your students won’t understand so they will get bored. If they get bored they start making noise. If they make noise then your lesson is ruined. New vocabulary items should be used when teaching them or when there is no other alternative (but there always is a simple way of saying things).
A couple of weeks ago I told my students a story and I was drawing the story on the board. I used new vocabulary but they got the meaning from the drawings. I used that listening activity for teaching new vocabulary with the help of drawings. So, if you use unfamiliar vocabulary then make sure your students understand it.
Learning a foreign language is difficult and learners are usually shy. Laughing at their mistakes doesn’t do anything but to aggravate the situation.
Sometimes their mistakes are so hilarious and it is very hard not to laugh. This is very embarrassing for students.
Today I had to test my students. The first topic was “directions” and the second one was “tell me a short story”. One of my students surprised me. For the first topic I asked: “How to go from ... to ...?” (The answer should be something like “go straight ahead then turn left/right ...”). He answered: “Go out then ...” Then I asked him to tell me a short story (students have a 5 row story in the notebooks as an example that starts with “A man and a woman were celebrating their ...”). The student answered: “A man and a woman go out ...” Of course, the whole class started laughing at him; definitely, not a very pleasant situation for him.
There are so many other things a teacher shouldn’t do in the class but these 3 are things that are usually done in the class and most of times unintentionally.