Excessive minimalism. Remove most grammar, and let the front and back sides be unrigorously related. I once read somewhere (Tatsumoto Ren's blog?) that dictionary definitions are often hard to parse, whereas when you use the word in a sentence, it's clear what it means and how the word works. Leave the precise definition and usage examples in an "Extra" or "Hint" field (I call it "Post-back" on my cards). Ultimately, the purpose of the Anki card is just to verify your thoughts, not really represent them.
Separate context from terms using (white)space, rather than italics/bold. Math symbols often use italicizing and bold in weird ways, as well as punctuation and things that look like punctuation. I used to make vocabulary and symbols bold, but this became confusing with vectors in math. Besides, if you make your cards extremely minimal, then formatting usually becomes unnecessary.
One exception is for my German language deck. I use normal for the German text, and italics for English (albeit very inconsistenly because it's a pain to change the formatting after copy-pasting from an online dictionary). But then the convention and context are limited enough that there isn't any confusion. For my other cards, I have one big deck for all my subjects, so I have to follow one convention.
If you have old cards that are inconsistently formatted, but you can read them fine, don't worry about changing them, unless it's a quick, thoughtless fix. For example, removing all bold or italics from a field can be done in about 5 keystrokes, i.e. E Tab Ctrl-A Ctrl-B Ctrl-B Esc.