Having an activity for students to do independently at the beginning of each class has great benefits. Students can transition into the class without being dependent on the teacher and will get them ready for class. Warm-Ups make the most out of the time students have in class. Students are no longer waiting for class to start as students trickle in or get their materials together. Teachers also don't have to be "On" the second the students walk in. They can finish up what they are in the middle of doing - talking with a student or another teacher, sending an email, gathering materials for the class.
Here are some ideas for Warm-Ups. In my school, we call the "Do Now."
Exit Tickets at the end of class
Exit Tickets are a great way tot check for understanding at the conclusion of learning. Here are some examples for Exit Tickets in the classroom: