Preview the texts and lab manuals for the class.
Find and inspect your lab and storeroom areas. Check: the materials lists and inventory, the location of the first aid kit, the location of outlets, switches, temperature controls, etc., the availability and procedure for obtaining audiovisual equipment such as overhead projectors, screens, erasers, and chalk.
Find out departmental procedure for ordering and obtaining supplies.
Become familiar with safety rules and procedures, emergency procedures, evacuation plans, and the layout of your building. Not only is this useful in the event of emergencies like fires, etc., it is vital that you understand that this is "tornado country" and in the event of such an occurrence, you will have to shut down your lab quickly and get to shelter.
Locate the primary lecture hall.
Understand exactly what the students are supposed to know/learn and why.
Perform the experiment yourself with an eye to how students will see it:
Prepare lab notes, materials, and handouts with this "dry-run" experiment in mind.
Start on time!! You should be there five (5) minutes before class starts, and if you don't start on time, you will run your students short at the end of the section, which is not good for you, them, the equipment, or their next instructor.
Explain the purpose of the class. Why are they doing this? How does it relate to the lecture? How long will it take?
Demonstrate the use and care of equipment, lab procedure, and any procedure which you think may be problematic. Make sure students are aware of any particular safety considerations.
Supervise student work. "Walk-about" management works well here and allows you to not only see how the students are doing but allows them to ask questions more freely. You are trying to promote critical thinking skills and scientific inquiry. It has been said that learning is a communal act, so encourage a wholesome and disciplined interaction, and don't feel too harassed when they all ask questions at once. Take the questions one at a time, and take note of them. You may have missed something, or they may just be asking good questions.
Summarize. Plan ahead to take the last 5 - 10 minutes to summarize and synthesize. Now is a good time to ask synthesis questions. How does this relate to other aspects of the subject? How would such a theory affect other systems?
Set deadlines for submission of lab results or projects. Clarify rules and format for reports.
Evaluate the overall success of the lab. What went especially well? What could have been done a bit differently? What procedures worked well - or not so well?
Consider the reports as a whole. Did the students understand the lab? Did any number of students consistently miss the same thing? While cheating is always a possibility, consider also whether you may have missed a point or not have effectively gotten it across to them. (Beware of paranoia.) Were they able to draw reasonable conclusions from the data?
Read, evaluate, and return lab reports in a timely manner with cogent feedback. Students can't improve if they don't know how they could have done better.
Allen, R. R. & Rueter, T. (1990). Teaching Assistant Strategies: An Introduction to College Teaching. Dubuque: Kendall/Hunt.
TAs As Teachers. (1978). Office of Instructional Consultation, University of California - Santa Barbara. Santa Barbara: Regents of the University of California.
"Back to the Lab". (March, 1989). The Teaching Professor, 3 (3), 3 - 5. Madison, WI.: Magna.