When students have ample opportunity to speak and communicate in English, they easily develop listening and speaking skills. They are also more able to connect with their peers and develop self-confidence, which is actually a huge part of learning a language.
To help encourage them to speak, create a supportive and accepting environment. When assigning tasks and projects, keep in mind the student's level of proficiency. Assign groups and introduce people with common interests and activities so that they have things to talk about other than school work.
Also, establish a classroom climate in which a student's errors are accepted as a normal part of the learning process. Make sure all other students in the class are welcoming and positive, offer their help, and communicate carefully with ESL students.
When students make several errors while speaking, choose one to correct, not all. Give priority to correcting errors that interfere or inhibit clear communication of ideas.
Speak clearly and pause often when speaking to ESL students and leave them plenty of time to formulate their own sentences. Encourage them to ask questions, answer your questions, and give their input, and share their ideas.
Learning to recognize and read and write a new language is largely based upon speaking a new language. Encourage ESL students to speak as often as they can. Communicate with peers, but also discuss lessons and any questions they may have.
This information is taken from Many Roots, Many Voice: Supporting English Language Learners in Every Classroom.