They're just words that modify a verb, and usually end in ly. Sounds pretty inoffensive, right?
Wrong. They're evil. Or at least that's what writers are often led to believe. I'm sure you've heard it all before--adverbs are a sign of weak writing, of telling instead of showing, of overwriting, etc etc. And I have to admit that for a long, long time, I hated adverbs too. Then I found out adjectives are to be hated as well, and so those also had to be used with caution. There are rules for a reason, right? I wasn't so overconfident that I thought my novels would be the exception to the rule.
But then something happened. Well okay, nothing really happened, but that sounded very dramatic, didn't it? What actually happened was that time passed, I grew as a writer, and I learned lots. And of all the advice I took in (and trust me, there was A LOT), this one bit stuck the most, so here I am to share it: Don't say something in ten words if you can say it as well, or better, in five (I can't remember/find the source, so my apologies for that).
Great advice, right? So now instead of focussing on adverbs and adjectives, I simply ask myself 'How can I effectively (ha!) say what I want to say in the fewest amount of words possible?' Sometimes this involves using a stronger verb in place of the verb+adverb. Sometimes this involves omitting an adjective that was unnecessary. Sometimes it's none of these things--it depends on the sentence. But yeah, using this question as a guide definitely cleared things up in my head.
So there it is, folks. Do with it what you please :)