When time permits, I add pictures to help students get a visual image of the question. Using pictures can be tricky, though because your idea of an illustration to fit your question may not click with your students. Funny animations can help liven up the PowerPoint, but they can also be distracting.
Spend about 15 minutes a few times a week reviewing terms using your PowerPoint presentation. Mix up the slides so that students will not get accustomed to the order of the questions. Add additional questions and remove the ones that the students know. Rephrase some of the questions so that students can apply the information that they are learning.