After presenting new concepts and a couple of examples which are very carefully chosen from a book or sometimes created by myself, I like to assign a problem/provide the demo of the lab/example and allow the students a few minutes to work on it, as I walk around and check on their progress. In this way, I can see where they struggle, correct their mistakes, and give them personal attention and encouragement. After that, I ask someone to come up to the board to solve the problem so that everyone can check their work. Sometimes, I prefer group-work to engage students. In such group-work, I usually give relatively complex problems such as word-problems and problems which demand more steps. After a few minutes, I ask one of the groups to present the problem on the board/ demonstrate the experiment