You will be speaking in a large room. Text on title slides should be restricted to 9 lines. Avoid white backgrounds. Color combinations with pleasing contrasts are preferable. Avoid dark slides and overly dark backgrounds.
Simple typefaces are preferable to fancy fonts.
Bold type may be effective on title slides. Vertical slides do not fit the screens. Use horizontal slides in all cases. Slides of scenes or organisms should clearly show what you want the audience to see. Never reverse the projector to return to an earlier slide.