Always ask yourself: “what can I remove from this chart”? Remove Excel defaults, remove grid lines, make the chart smaller, use soft colors, remove irrelevant labels, remove the legend (by directly labeling series), remove series that you don’t really need, remove frames, remove decimal places, remove visual fluff.
Then ask yourself: “what can I add to this chart?” Add meaningful annotations, add other charts, add change, add interaction, add a story, add you.
“Perfection in design is reached not when there is nothing more to add, but when there is nothing more to remove”… Antoine de Saint Exupéry