At the beginning of every class I have a bell ringer or warm-up question. This has not only pedagogical benefits, but classroom management ones too! For one, the kids know at the start of every class they are to be quiet and working on something. It gives me time to take attendance, get my mind focused on the lesson and take care of odds and ends with each class. Typically, my bell ringers are a DOK 1 or 2 question from the previous day's lesson. I want to "step-up" the thinking on these but it's hard some days to think of something! Recently, I came across this article from Edutopia (George Lucas's Educational Foundation). It has tons of ideas for bell ringers; I encourage you to check it out!