There are two possibilities if you are teaching ESL to students. One is that they haven't learned to tell the time at all, either in English or in their first language. Or, more likely, they will have learned to tell the time but need to understand the English words and phrases that are popularly used for understanding and telling the time. However, the steps will be the same for both groups, perhaps just a little easier for the latter.
In the first part of your lesson, don't show the students the more-difficult aspects of time telling. Begin with on the hour. They can probably count and recognize numbers up to 12, so it’s just a case of showing the big hand and little hand pointing to respective numbers and understanding what the term o’clock means. You should then practice until the students understand and can identify what the time is when it is on the hour.
Once the students have learned the notion of separate hours, you can move to the second part of the lesson, getting your students to associate basic hours with daily routines and activities. Ask them what time they get up, and have them answer to the nearest hour. Then ask them what time they go to school. This exercise is an important part of the learning process, because it moves beyond repetition and simple counting to a more-cognitive activity -- associating times with activities.
Once your students have a clear grasp of general times and can associate them with particular activities, it is time to ask them to be more specific. Begin by asking them between which hours they do certain things. For example, you can ask whether they eat breakfast on the hour or between hours. Then ask them to say the hours between which they eat, go to school and play. Once this has been mastered, you can show them the five-minute intervals on a traditional clock face, and narrow down the times that they do those things. Then, when this has been understood and mastered, you can move onto single minutes.