Write down everything that needs to be done in your classroom regularly that could be done by students instead of by you. These include things like passing out assignments, cleaning chalkboards and anything else you can think of.
Create a job program so that all students understand that some students are going to be assigned certain tasks and expected to complete them.Be clear about the rules of the program rather than arbitrarily picking students to be helpers in order to avoid resentment or complaints about fairness.
Make it a requirement that a student must show good behavior to get a classroom job. Students usually clamor for the opportunity to do a task such as hand out the papers when a teachers asks one student at a time to do it, so make it clear that those with ongoing good behavior will have ongoing jobs.
Assign a rotation. That way students get a chance to try different jobs and jealousy won't erupt over one student getting to do a job that another wants, because you can assure them that as long as they follow the rules, each will get a turn.