Adjectives and adverbs are best used sparingly, in my opinion. This is especially true for adverbs, where it is almost always the case that the adverb is a stand-in for some other, stronger verb the writer hasn’t thought of. Sentences with many adverbs tend to become over-modified and lose their impact. Take the example of a jet flying overhead: the point is to make sure the reader knows it is loud. You could write: “A jet roared overhead.” “Roaring” is loud, I suppose, but how loud? If you were to add an adverb -- “A jet roared loudly overhead” – you haven’t done much; “roars” are generally loud. You could change roared for another verb: “shrieked,” “boomed,” “howled,” “thundered,” and so forth. Each verb has a different flavor, and conveys a different sound to the reader. But to really get the effect of how loud, you have to show what happens because of the noise: “A jet roared over head, causing the chandelier to swing overhead and the flat champagne in our glasses to ripple.”
Adjectives are a little different, but again, to me, the way to make things clear to a reader is to be as concrete as possible. Adjectives can be fun, but like adverbs they can make things abstract. In the example sentence above, I used an adjective, “flat,” to describe the champagne; this adjective does a kind of multiple duty – first, it helps us see the champagne; if it was just “champagne,” most readers would have a different image in their heads – second, it provides a small hint about what might have been going on in that room, since, if the champagne is flat, it obviously had been sitting in the glasses for a while – and third, it conveys a certain emotional quality: champagne is a festive drink, but flat champagne means the party is over. Of course, I could have piled on more adjectives (if one is good, three or four must be terrific!): “A jet roared menacingly over head, causing the impossibly ornate chandelier to careen back and forth, while the flat, pinkish remains of the champagne sloshed in our glasses.” (Extra credit to me for using an adverb to describe an adjective!) You can see that while it is possible to really pile it on, the cumulative effect of such sentences is to exhaust the reader and to divide attention – since everything is modified, what one thing in the sentence is the reader supposed to notice?
So, to summarize, adverbs are generally best left alone; when you feel the need for an adverb, try to think instead of a strong verb that can get the same idea across; adjectives, when used sparingly, can add clarity and focus, and serve as a way to convey tone or attitude and direct attention.