Reusing your existing slides can be a great help: first you need not recreate stuff you already have and secondly you are saving so much time that you can use more effectively to practice your presentation! Having said that, always start by creating an outline of your presentation. This is important because it gives you an opportunity to plan your slides all over again. Thereafter, reuse any existing slides. PowerPoint provides a quick command that locates specific slides, and enables you to add them to the active presentation.