Fungi can be interesting to observe, but not all of them are healthy and molds that have spoiled food are particularly a problem.
Alcohol is a solvent of choice for preserving specimens. Alcohol, however, causes some specimens to shrink.
Pond water is a favorite sample to observe. Sometimes, you do not see anything, however. The reason is usually that you took a sample from the water itself and not of the ground.
A drop of inorganic fertilizer greatly enhances the growth of algae in a mini-aquarium.
Small air bubbles in the slide are not generally a problem but can be avoided or reduced by several methods.
Objects for microscopy must be sufficiently thin, translucent and must have a sufficiently high contrast.
A slide box with ready-made permanent slides gives you already many interesting things to look at.
Squashing the specimens (instead of cutting them) is a fast and easy way to prepare specimens.
Is it possible to use microscopes to identify pathogens, such as the EHEC bacterium, which currently (May-June 2011) causes problems in some parts of Europe? The answer is, unfortunately, no.
A simple check of the refrigerator (or the super market) provides many safe sources for microorganisms to view under the microscope.