PowerPoint has pre made stock layouts that are already set up for accessibility.
The correct slide layout is probably the most significant step that can be taken to ensure that the slideshow will be accessible.
While you can drop content any place on the slide in a variety of ways, only when you use the "Title" and "Content" areas can you ensure the information will be presented to assistive technology.
It is highly recommended to avoid the use of Text Boxes (from "Insert" on the menu bar). Any content placed in these boxes may be lost to assistive technology.