A graphical abstract is a single image that tells the main message of your paper. Readers see it in the journal's table of contents before they read a word, so it should be understood in about five seconds.
Start with text, not pictures: “We made X, tested it in Y and found Z.” Every element in the figure should support this sentence. Anything else goes in the paper.
Most graphical abstracts read like a comic strip: problem → method → result. Three or four stages joined by large arrows are enough. Keep the same icon for the same thing everywhere.
Use labels of one to four words. Avoid full sentences, long chemical names and statistics. If the text is too small to read when the image is shrunk to a thumbnail, it is too small.
Pick three or four colours with a clear meaning (for example, red for disease and blue for treatment) and use a colour-blind safe palette.
Publishers give a size, file type and sometimes a minimum resolution. Many prefer a wide image. Export a high-resolution PNG or TIFF, and keep an editable SVG or PDF so you can make last-minute changes.
Open the Graphical Abstract Maker, type your one-sentence story and pick “Wide 16:9”. You can then ask for changes such as “make the arrows thicker” or “add a mouse icon in stage 2”.