OpenOffice.org Impress: Using Master Slides
The Master view in Impress is the equivalent of page styles in Writer. It's the view where you can set elements of design that appear throughout your presentation, such as the slide background and foreground colors, any reoccurring elements, and the fonts. By creating the master slides you need before you add content, you can automate your work and free yourself to focus on content.
Master slides are quick to learn. But the real trick to using them well is not a deep understanding of the software, so much as a sense of modern design. The stylized form of a presentation does not alter the concepts you use to design one, any more than the limited space of a business card affects how it is designed. Both use the same basic elements as any modern design project, such as contrast of different elements, the alignment or proximity of related ones, and repetition of the look and location of reoccurring elements.
Moreover, if all else fails, you are unlikely to go far wrong if you keep your design as simple as possible. For most purposes, you can treat a slide as a special case of online design, little different from designing a web page except that you don't need to struggle against the limits of HTML.