This is an inspiring article series that gives some tips and tricks on how to motivate students to give their best on classwork.
One of the most important tips I agree with is to "Stop Giving Trash Can Work." Have students create something that is going to make a difference. Having authentic assessments that has a real-world impact often motivates students to do well. Students should know that they are not just doing this for me (the teacher). Others will see this work as well. Whenever my students know that their parents will see the work they are creating, I almost always see an increase in, not only work quality, but in creating memorable and personal learning experience.