A scientific figure + legend/caption should be able to stand independently of its accompanying paper. As such …

• If you have a question about a figure…
  • Before you Google, go to the legend!
    • (Or Google if you want to see how many irrelevant things an acronym used could stand for, but doesn’t in your case…)
  • Search for all places the figure is referenced.
    • Command/control + F is your Friend! If looking for Figure X, search for both “Figure X” and “Fig. X”
• All acronyms and abbreviations must be defined anew.
  • Unless generally recognized as established convention (e.g., DNA)
• Line &/or symbol styles, coloration, etc. must be described.
  • And, ideally, they’re colorblind- & black/white printing friendly.
• Meaning of error bars, asterisks indicating statistical significance levels, etc. must be explained.
• Sufficient methodological information must be included for the reader to interpret the figure.

The first (usually bolded) sentence typically serves as a title and often conveys the key takeaway of the figure.

When writing figure legends (captions) …

• Make sure your legend can stand alone.
  • Define all acronyms, abbreviations, line styles, statistical significance indicators, etc.
  • Include sufficient methodological information for readers to know what they’re looking at and interpret the figure.
• Minimize effort required of the reader
  • Don’t step out of line! (Align your figures, axes, etc.). See https://bit.ly/adobe_illustrator_fundamentals
  • Make the font large enough to readWhere possible, include labels in the figure (rather than making the reader consult the legend).
  • Use a consistent coloring and formatting scheme throughout your figure panels and figures.
• Make and use your figures purposefully to tell a story.
  • Start with a bolded title/summary statement of the key takeaway.
  • Cite each of your figures in your main text and number (and place) them in the order in which you cite them.
    • e.g., We found X correlated with Y (Fig. 1a) but was independent of Z (Fig. 1b)… To follow up, we performed… which showed… (Fig. 2).