Students, staff and researchers need to prepare posters from time to time and we provide workshops on this.
I attended one yesterday and it was interesting to be made aware of what should be considered even before starting in order to make the poster eye-catching and communicate what you aim to.
The facilities available in PowerPoint make it an easy tool to use for this purpose.
Setting up the size at the start, using grids and guides and zooming in helps for getting the layout right.
Its best to keep it simple and concise, use easy-to-read text and attractive images and look at the flow and balance of the overall poster.
This is a useful site about what makes a good or bad poster:
Here you can find more information about colours to use, contrast, fonts and typeface for accessibility.