Slide headings should be centered and font size 36, Helvetica or Arial
All major phrases and words in the slide that you want the audience to see should be between 20pt and 24pt.
Axis tick labels and minor details should be 18pt.
No text should have font size <18pt. If you want to de-emphasize text that is less important, change the text color from black to grey. If you want to emphasize text, make it bold or use a text box around.
Design slides in Inkscape.
Make all text editable by exporting figures as PDFs from R or Python.
All schematics should be made as scalable vector graphics rather than bitmap images so that they can be used by others in the lab.