Key to powerpoint presentations: Keep it simple.
A lot of people use different slide transitions for every page, plus they have different transitions for each bullets of every page, plus they add pictures all over the place. OK, so you know how to use powerpoint. Big deal. Trying to make the presentation interesting by using effects can easily be overdone. People who watch your presentation actually focus their attention on your effects and not your content so it's really not what you want to do.
Myself, whenever I do presentations, I pick the them (slide template) and I apply a single transition to all my slides. I never do any bullet transitions because they anoy me to death, and I would rather focus on what I have to say instead of focusing on my mouse. Pictures aren't a bad thing as long as it's used moderatly. For example, if your total presentation is composed of 4 major sections, you may consider adding a picture at the end of each section, as long as the picture relates to your content.