Pronunciation is a really important part of teaching ESL. It is often the focus of speaking or listening exercises but you can even include pronunciation practice in writing exercises by asking students to match words that rhyme for instance. This pronunciation worksheet, for example, contains flashcards you can use to help your students learn different sounds. It is one of 209 free worksheets available in the pronunciation section of the site. Take a look at other worksheets to find what you and your students are working on. You can even narrow your search if you are looking for worksheets on homophones; intonation, rhythm, and stress; and tongue twisters.
Students need a lot of practice with pronunciation. In many schools reading, writing, and grammar are stressed while speaking, listening, and thus pronunciation are not emphasized. Since learning English is all about communication, it is important that students have practice using their language skills. Poor pronunciation can prevent students from being understood and hinder them in interactions with others. You can practice pronunciation through choral repetition during the introduction stage of your lesson and model the proper pronunciation of words when students make mistakes.