Give your students other slides to explore. The mosquito head ones are a huge hit in my classes. Get them to collect their own samples to look at. The more your students use microscopes, the better they will get at it.
I try to incorporate microscope work into as many of my lessons as possible. If we are studying plants, we will create nail polish stomata slides. When we study gas exchange, we will look at the tissues in the different parts of the respiratory system. Blood vessels and blood smears are a must when studying the circulatory system. The possibilities are endless.