How important are the visuals in a presentation? Vitally important. And the importance goes both ways: Excellent visuals can bring life to your presentation story, while poor visuals can take away from your story. Which choice do you make?
The guiding principles when incorporating a slide into your presentation are that it must advance your discussion and clarify the concepts you are explaining; it must ideally add a non-verbal representation of an important concept; it must be crystal clear and easy to navigate from the point of view of the audience member.
The language on each slide should be grammatically perfect. If you are a nonnative speaker of English and you are not sure about the grammar or punctuation, ask someone for help.
It is a very important exercise when selecting and building slides to differentiate for yourself what you (the speaker) need to know from what the audience needs to know.
You may feel, for example, that you have too many slides in your introductory section. Ask yourself: Who needs these slides, me (the presenter) or the audience members? Am I using these visuals to help myself remember the story — which is okay to a point — Or do I need to be more familiar with my material so that I can eliminate slides that are unnecessary?
This thinking can be applied to the entire story: In general, which parts of the story can I tell without using bunches of slides?
The audience should not have to work hard to understand our story and our visuals – – it is our job as presenters to work the hardest.
Here are some examples of excellent visuals – –

From a talk entitled “Sketch Recognition” by Computer Science PhD student Jeffrey Browne, UC Santa Barbara.