It is refreshing for the students to work with a different teaching style from the professor's, so your words will serve them well. There are many possible styles for presenting quiz-section material. Styles can range from lecturing to round-table discussions. You can work problems in front of the class, or you can have students work problems. You should try to avoid simply rehashing the lectures.
Developing a successful teaching style requires practice. Success with a particular style also depends a great deal on the type of students you get. If you have difficulty encouraging your students to participate in class, you need to be prepared to cover course material (i.e., lecture). If you get active students, great! Try to generate discussions, prompt them for questions, etc. It is generally not a good idea to structure quiz sections very loosely, however. You will appear disorganized and it will most likely be difficult to inspire participation by your students.
Holding organized discussions on major course topics is a nice style for advanced students. Have a list of issues to discuss in the event that students have difficulty maintaining the discussion or drift too far from the topic at hand.
Such discussions do not work well with most groups of students, however. You will most likely need to lecture for at least part of each session. Lecturing from overheads is the most structured style. You can cover lots of material, but students can be easily overwhelmed. You should use this technique to cover long examples. Writing out long code segments requires a lot of time and kills the momentum of the session. If you want to slow the pace of the class, you can lecture from notes on a whiteboard, chalkboard, or overhead film. This technique gives the students more opportunities to ask questions. Face the students when you talk to them.
It is a good idea to cover administrivia and to return assignments or exams at the beginning of class, especially if you plan to discuss the assignments or exams. Students are generally unfocused and distracted at the beginning of class and a few stragglers always arrive late.
Following administrative tasks, present your outline for the session. This lets the students know what you want to discuss. Give them the opportunity to raise other issues. You can discuss the issues immediately, or add them to the outline. However, if you delay discussing their questions, make sure you reserve a few minutes at the end of the session to deal with them. Otherwise, the students may feel as if their concerns are being ignored.
In general, you may invite questions about homework, programs, and lectures at the beginning and/or at the end of section to give them a chance to direct the progress of the session, but if no one asks a question quickly move on.
Also pause for questions throughout the session. In the undergraduate classes, especially 142/143, the students may hesitate to ask direct questions, either because they don't know the actual extent of their ignorance, or because they're too shy. Try to make it easy on them by suggesting trouble spots. Posing questions of the form ``can someone tell me what XXX is?'' can work well even on a college level.
You should deal with the most important topics first, leaving more flexible activities for the end of the hour.
If a recent lecture covered difficult or confusing material, go over it again filling in all the details, whether or not they appear in the lecture notes or syllabus.
Examples are your most important and effective tool for conveying course concepts. Try to include a few examples when discussing complex or difficult topics. Even trivial examples can help, but throw some more difficult examples at the students, too. Work problems based on recent material, especially ones likely to be seen in homework assignments (if applicable). Having the solutions worked out ahead of time helps. You can work the problems in front of the class, or have students work the problems at the board/projector or in their seats.
Self-assessment exercises are a good tool for students to judge whether they are keeping up or not. Once a week, give the students a problem to work out that you believe requires a fair understanding of a recently learned topic. Give the students about five minutes to work on the problem, then present the solution. Don't embarrass students by calling on them to give the answer. Constructing a problem that is not too difficult nor too easy is difficult at first, but after a few weeks of practice you won't have any trouble with it.
Here is an example outline of a typical session:
No matter what style you plan to use, be well prepared. You should allow yourself between one and four hours a week to prepare for quiz sections. After you do it a few times, you'll know how long it takes you. You should think about what you need to say and how you will say it. You should makes notes and/or overheads, including an outline of what you expect to cover and how long you expect to spend on each topic. Remember that pictures and diagrams are extremely helpful, and include these in your notes as well. Also, write down a few examples on different topics and their solutions. Expect to cover one or two, and reserve the rest for questions on those topics.
If for some reason you have no material to cover, either cancel that session or turn it into an extra office hour for that week. This should rarely occur. Even during the first session you should have plenty of material and course details to discuss.