Which text styling should I avoid on an ATS-friendly resume?

Avoid styling that changes how the characters are stored, hides text, or makes text hard for people to read. The main ones:

• Decorative, script or novelty fonts, and icon or symbol fonts for bullets.
• Text effects such as shadows, outlines, glows, reflections and WordArt.
• Text turned into images or outlines.
• "Fancy" letters copied from text generator websites.
• Strikethrough, highlighting and hidden text.
• Very light, very small or very thin text.
• Letters spaced out with typed spaces.
• Emoji and decorative symbols in place of words or bullets.

What is fine: a standard font, sensible sizes, bold for headings and job titles, occasional italics, one accent colour, simple round bullets and normal capitalisation. These keep your resume readable for both software and people.

Whatever you choose, finish with the copy-and-paste test on the exported PDF: if the pasted text matches what you see, your styling is not causing problems.