Best Practices for Working with the Cells
It is best not to merge a lot of cells because users of screen readers have a harder time understanding what is in the excel sheet. The screen readers don’t know what order the information should be read in.
It would be best to have a cell be a title for the numbers or words that will be underneath to explain what this data be shown means.
Best Practices for Font
Try to use the automatic black font when typing because it there will be very few color contrast issues.
Best Practice Overall
It would be best to go over this article How to Create an Excel Sheet That is Accessible to Everyone (Desktop Mac) or How to Create an Excel Sheet That is Accessible to Everyone (Microsoft 365 Web App) because it has a lot of useful information on how to use some of the key accessible feature inside of excel.
It is also best, to give each sheet a unique name to limit any confusions for someone who is using a screen reader.
When using tables, graphs, or any other way to show data try to use headers and keep it simple so a person using a screen reader can easily identify any information that is be conveyed.
The information gathered for this article comes from Microsoft How to Create an Accessible Excel Sheet.