The difficulty with adverbs falls to the familiar saw about "show, don't tell": If the adverb is instructing the reader how to interpret the action, the implication is that the description itself is weak.
- "I'm ready to go," he said.
- "I'm ready to go," he said mischievously.
- "I'm ready to go," he said mournfully.
These three lines read very differently from each other, even though only the adverb is changed. And the reason they read differently from each other is not because they describe different things, but rather because the reader is explicitly told how to interpret each one of them.
The problem with relying on adverbs, then, is the problem of telling your readers how to feel rather than actually creating that emotion in them; the problem of telling your readers how a moment or a glance should be understood, rather than portraying that snippet in a way where they, themselves, would understand it.
At its worst, you can have the reader feel that he's being implored to think of the characters as being heroic and heinous and hilarious and horrific, without the text ever actually showing any of those things.
In this way, swapping
she said wryly for
she said with a wry grin is no substantial improvement; you're still simply cuing us how to understand the statement.
Here are some alternatives where the difference is much greater:
- Change the text being spoken, so the wryness is self-evident and doesn't need to be brought additional attention to.
- Bring the wry expression to life - instead of just saying that it's "wry", tell us that it's the same grin she makes when her baby soils itself, or that she's just barely keeping from cracking up. Something that makes the expression vivid and concrete.
- Bring the situation to life - tell us what the use of wryness means to the speaker, or the viewpoint character. "It took me a split-second to realize she was joking"; "I know she didn't mean to sound mocking, but it grated on me anyway."
All that being said, though, "telling vs. showing" is a constant tradeoff, a balance, not something to always decide in the same way. In plenty of cases, using an adverb is a simple, effective way of communicating something. It's not wrong to sometimes use adverbs; what's wrong is to use them as a replacement for vivid descriptions (or in addition to better descriptions, in which case they're just unnecessary).
Here's a quick checklist you can use to consider any particular adverb use.
- If I take the adverb out, does the line still work? If yes, it's unnecessary; cut it.
- Can I rewrite the line so as to eliminate the need for the adverb? If yes, that's likely to be better, crisper. "Yell," instead of "say loudly"; say something actually wry, instead of saying a colorless line "wryly."
- Does the adverb get across a clear image? Sometimes adverbs are an integral part of the language. "Walking briskly" has a very distinct feel to it, in a way that "walking," jogging," and "perambulating" don't, and also different than other things one might do "briskly." "Walking briskly" is kind of it's own thing. It's very reasonable to use adverbs this way -- the only concern is that such phrases are fairly likely to be cliches, so in that sense, they shouldn't be overused.
- Is it important for me to describe this vividly? If yes, then this is a case where you want to show rather than tell; this is not the place for an adverb.
- Have I been relying on adverbs a lot to get across tone and atmosphere? If so, that could be an issue with your writing style, and you might want to pay attention and see if you can improve in the next draft.