Just as there should be no extra slides, there should be no missing slides.
As a rule, you shouldn't speak for more than a minute or so without having new information appear.
(Also see my advice on giving a job talk and on making a technical poster.) There are many good references regarding how to give an effective talk — that is, a technical presentation, whether at a conference, to your research group, or as an invited speaker at another university or research laboratory. What could you have told someone about the topic, 30 minutes after the end of the presentation?
This page cannot replace them, but it does briefly note a few problems that I very frequently see in talks. One of the most effective ways to improve your work is to see the reactions of others and get their ideas and advice. Before you start preparing a talk, you need to know your goal and know your audience.
Unfortunately, you are probably not one of them, at least not yet.) As a particularly egregious example, do not discuss a user interface without presenting a picture of it — perhaps multiple ones. Do not use the same title on multiple slides (except perhaps when the slides constitute an animation or build).
As another example, you should not dwell on the title slide for very long, but should present a picture relevant to the problem you are solving, to make the motivation for your work concrete. Choose a descriptive title that helps the audience to appreciate what the specific contribution of this slide is.
The goal of a talk you give to your at a university, you want to encourage questions, you have more time, and you should plan to give more of the big picture.
The goal of a talk is similar to the goal of a technical paper, so you should also read and follow my advice about writing a technical paper.
That does not mean holding back important details — merely omitting less important ones.
You may also find yourself omitting entire portions of the research that do not directly contribute to the main point you are trying to make in your talk.