Anything of the "Never use adverbs" school of advice - advice that absolutely forbids a certain writing tool. I tend to think it's of more use propping up insecure writers (who can read other people's stuff and scoff at how it breaks the rules) than as actual writing advice, because as advice it's rather paralyzing. Look! An adverb! Kill it with fire!

Besides, advice like that is really dependent on the prevailing style. Eyes like gemstones are out of fashion now, and it's good to know in advance that there are readers who will dismiss your work out of hand if you describe your heroine's eyes as shimmering opals that change color with her feelings (shadowy sapphire for sadness, sparkling turquoise for joy, and of course shimmering amethyst when sympathy o'erflows her soul) - but that doesn't mean you shouldn't do it if you really need to.

(I also answered "best writing advice" below.)