Use an off white background - for example in LaTeX \usepackage[x11names]{xcolor} \setbeamercolor{background canvas}{bg=Seashell1}
Check the colour contrast on slides and text - there are free tools like https://colourcontrast.cc/
Use a sans serif font
Show the total number of slides and the current slide number
Avoid walls of text on each slide and use slide transitions to reveal sections of text as needed
Avoid relying on colour alone to highlight - for example use italics to highlight text, and in diagrams use different shaped nodes or dotted/dashed lines
Make sure to finish on time
Be mindful of speed for anyone taking notes
Read out everything that appears on the slide including equations
Explain/describe any diagrams or images
When including links label them appropriately - for example “my webpage” as opposed to “click here”
Provide alt text for any images - https://accessibility.huit.harvard.edu/describe-content-images
Consider using some of the accessibility packages that LaTeX offers
Provide the handout version of the pdf by replacing \documentclass{beamer} with \documentclass[handout]{beamer}