Best practice is to use sans-serif fonts, rather than serif or decorative fonts. Sans serif do not have the decorative lines. The fonts would include Arial, Calibri, Century Gothic, Tahoma, and Verdana. The font size should be 24 pt font for the body text. The font could be larger depending on the audience or page layout.
When creating Graphs or Charts in PowerPoint, you want to make them as accessible as possible. By following this guide, you will be able to make your content as accessible as possible.
Alt Text and Descriptions
Right Click on the Graph or Table (on empty space, not on data) and select "Edit Alt Text..."
Fill in the information into the newly opened field.
By including a description or Alt-Text of the information portrayed in the Graph you can get the information across to those who may be using Screen Readers or an interpreter. This same idea should also be applied to images as well.
When using a graph the alt. text should be a quick overview of the graph, a long description of the graph should be added near the graph, and finally an accessible table with all of the information should be included somewhere How to Create Accessible Tables.
Keep Things Simple!
A Graph does not need to be overly complicated (And should not be!). Try to keep your data as clear and concise as possible! Some things you should look for is:
A basic and accessible color-scheme with Good Contrast. Typically, Black and White is the best option when it comes to contrast.