I am a certified TESL teacher, though I haven't taught in years. I found that for beginning, and even intermediate speakers the best excercise is, "How to Make a Peanut Butter Sandwich."
Bring a jar of jam, a jar of peanut butter, knifes, a plate and bread to class. Then you simply ask, "How do you make a peanut butter and jam sandwich?"
Your goal is to have students describe ever step of making a pb&j. For example:
First you open the bread bag. Then you take two slices out of the bag and put them on the plate. Then you take the lid off the peanut butter jar. Then you pick up the butter knife and use it to spread the peanut butter on the bread.
This allows students to get the hang of some of the most commonly used verbs in conversation and allows them to pay attention to the idiosyncrasies of verb uses that don't make a great deal of logical sense in English.
Plus it starts out really fun when they say, "Put peanut butter and jam on the bread and put them together." Then you put the unopened pb & j jars on top of the bag of bread and attempt to eat it. It doesn't work so well. :) Good luck!
ps. # 1 most simplest and hardest thing that you MUST do while teaching ESL? Cut every idiom out of your speech until you are teaching them directly. They are wickedly confusing otherwise.