I realize that it is rather presumptuous of me to disagree with Mark Twain.
But Mark Twain once said: If you find an adjective, kill it.
I agree that there are some adjectives that deserve a quick and painful death:
1. Adjectives that can be replaced with action.
Kill those guys.
Think action, action, action (which translates to, um, verbs).
Here's an example (albeit, a rather lame one): instead of describing the sidewalk as being icy and slippery - have the character slipping and sliding and falling.
2. Adjectives that can be replaced with showing.
Kill those guys, too.
For example, instead of saying he had a messy bedroom, for pete's sake, just show the darn room - you know, with the bed unmade and the pizza box on the floor and the clothes all over the chair and etc. etc etc.
So where do I disagree with Mr. Twain?
I think that adjectives that are part of the showing process and that are specific...
....and that aid in the job of visualization (i.e., help the reader see the image clearly and specifically)....
...deserve to live.
Do not kill them.
Here's an excerpt from How to Steal a Dog. Imagine this scene without adjectives:
The house smelled damp and moldy. The floor was littered with leaves and corns. In the front room, a lumpy couch stood underneath the plywood-covered window....Stacks of yellowing newspapers were piled in one corner. Two empty cans of pork and beans sat on a rusty wood stove. I followed Mama into the kitchen. The cracked linoleum floor was sticky and made squeaky noises as we walked across it. I wrinkled my nose and peered into the sink. Twigs and dirt that had fallen through a hole in the ceiling floated in a puddle of dark brown water.