Organise and design your slides in such a way that they are your guide while presenting. A given slide should prompt you as a speaker with what you meant to explain. If, while practicing, you notice that you tend to skip something in your text, add something to the slide to remind you.
There are many different slide designs to choose from. Keep it simple and professional, but more importantly: keep it consistent throughout your presentation. If you are presenting at an important event on behalf of the university, please see the UU site for the corporate template (“huisstijl”). Programs that are often used for making presentations are PowerPoint, Keynote, Prezi, Poster, etc.