Light or dark background?
In bright rooms or with low-power projectors, a light background with dark text is easier to read. Dark backgrounds work well on big screens in dark rooms, but the text needs to be light and large. If you don't know where you'll present, go with a light background.
Just one accent color
Save one accent color for what you want the audience to remember: a number, a takeaway or a key word. If everything is highlighted, nothing stands out. Everything else can use your text color or grays.
Use the same colors in your charts
Give each category the same color on every slide: if “2025 sales” is blue in one chart, keep it blue in all of them. Don't let a chart rely only on red and green, since many people with color blindness can't tell them apart.