We often have so many things to teach our students we lose sight of how this knowledge was assembled. Thus science becomes a bunch of facts to be memorized, versus an ongoing process of understanding the Universe. I often will focus a little less on detail - after all that's what the textbook is for, and really go into depth and explain what people believed before, why they believed it, what people observed, and what the consensus that developed out of these observations were.
Along a similar vein, I will sometimes put the students in the drivers seat, show them the evidence that scientists observed and ask them to come up with explanations which explain what was observed or evaluate current scientific theories (such as evolution) using this method. I find that when students evaluate evidence for themselves it helps provide that "road to Damascus moment" that perhaps what they were taught at home doesn't explain the evidence quite as well as current scientific theories (even if they are a bit controversial in certain sections of society).
Additionally, as much as I can, I try and keep my assignments relevant. Rather than an abstract assignment with no personal stake for the student - I try and ask them what they should do in a real world situation. For a recent microbiology class I taught at another institution, I asked my (mostly nursing) students to come up with protocols to stop the spread of a hospital based infection throughout their ward.