The interactive lectures on this site have been designed to actively engage the students because Physics Education Research has demonstrated very clearly that this is the only way your students will really learn. The learning experience has to be structured so that the students can confront their preconceptions and build new mental models. This is especially difficult and important in modern physics where the concepts are so counter-intuitive and abstract.
The lectures have many multiple-choice questions imbedded in them to allow for Peer Instruction, a technique developed by Eric Mazur. To get the most out of the questions, you should provide each student with a multiple-choice booklet that has the first four letters printed on separate pages. Encourage all of your students - not just the few keeners - to show you the letter that they think is correct. Now you have a snapshot of the present understanding of all your students.
Next, there are a variety of things you can do depending on the responses that
1) If the answers are all over the place, you might want to reword the question, provide a bit more information or suggest a way of approaching the question.
2) If at least a third have the right answer, you can have the students turn around to find someone with a different answer and discuss their reasons with each other.Generally, but not always, this results in the number of right answers increasing. The ones that were 'right' will understand their reasoning better after explaining it to a fellow student. The other student gets a private tutorial where they can feel comfortable asking for clarification.
3) If almost all the answers are right, you don't want to spend much time on the question. You might choose a a couple of students to explain why they chose the 'correct' answer.
When it goes well, you don't need to explain anything yourself and all your students will be awake and involved.
The structure of the lectures was also inspired by Interactive Lecture Demonstrations developed by David R. Sokoloff & Ronald K. Thornton. These are similar to the Peer Instruction techniques but with two differences. First of all, the questions are specifically tied with demonstrations involving computer probeware, so that answering the question involves checking to see what nature has to say. There aren't many opportunities for this in modern physics, but these lessons have many demonstrations involving classical physics that is related. Secondly, the authors emphasize the importance of having students write down reasons for their answers - not just the answers. To this end, the worksheets have space provided for writing the reasons for the answers.
One tool that is really helpful in active learning are whiteboards.