The best way to ensure that your uploaded SlideShare displays as close to your original file is to upload it as a PDF. PDF files will provide the highest quality and ensure that custom fonts, images, and layouts will be retained. More details on the supported formats can be found here.

However, if you cannot upload a PDF, or you need to upload the original file, there are some steps you can take to ensure that your file displays as much like the original as possible. Instructions on this can be found here.