Give your students this Google Form (completely editable) to help both you and them reflect on this past school year in your class.
 
I included some fun questions and some deeper thought questions (20 total) to get you started. Feel free to use it as is, or change it up to meet your needs. 
 
I suggest explaining the purpose of reflection to your students and how much their input means to you first, and then giving them about 10 mins to complete.