I think it is important to cover the principles of optical microscopy because this tool is used so commonly in inspection in industry. It is also used to prepare samples for SEM or AFM analysis. For the first lesson I want the students to be able to use a couple of different scopes. Make sure you have enough scopes in your lab for the activity. If you only have a couple you may be able to have the students work on a computer project while some of them are using the scopes.
As far as theory goes I want them to be able to do a magnification calculation, a Snell's Law calculation and a thin lens calculation. This section also gives me the chance to talk about quantum dots because they are used for coloring samples.
Most of my students will not have biology until second semester so they may not have used a microscopy before.
There should be quite a bit of information on optical micrsocopes out there. One of the most comprehensive microscopy sites is Nikon's Microscope U: