A few basic rules about writing dialog:
(1) wherever possible, use “said” instead of an alternate. Usually you don’t want to draw the reader’s attention to the tag line:
“So what?” he said.
“So what?” he declared.
In the first case, you don’t really register the “said” while you’re reading — it’s a signal rather than a real bit of language. This is usually the better choice, although there are times when you need to draw specific attention to the way things are being said. You might find sometimes that using a tag other than “said” –called a not-said tag here– is effective.
“You ruined my hat!” she cried. “You’ve broken the feather!”
“You ruined my hat!” he roared. “You’ve broken the feather!”
(Note I’ve used exclamation points here. I’m trying to make something clear, so bear with me.)
This leads us to the second rule:
(2) avoid adverbs. Those -ly words will cause you to trip and fall all over yourself.
“You ruined my hat!” she said angrily. “You’ve broken the feather!”
“You ruined my hat!” he said furiously. “You’ve broken the feather!”
You don’t need these adverbs, especially not with an exclamation point. Trust your reader to get some things without hitting her over the head with them.
Now that we’re wallowing in the mire, we might as well go all the way: you can compound your sins, if you really are feeling self destructive. Pile it on:
“You ruined my hat!” she spat angrily. “You’ve broken the feather!”
“You ruined my hat!” he roared furiously. “You’ve broken the feather!”
Now you may be saying: But I like adverbs. I love exclamation points. I sleep with a dictionary under my pillow, and I’ve got all these great synonyms for “to say” stored away, tucked into corners everywhere. To which my reply: Go to it, then. Like most things having to do with writing fiction, this is a matter of aesthetics, and all aesthetics are personal.
Now on to the final point.
(3) Play with the rhythm of the dialog (and everything else, too).
“You ruined my hat. You’ve broken the feather!” she cried.
She cried: “You ruined my hat! You’ve broken the feather!”
“You ruined my hat,” she cried. “You’ve broken the feather.”
Read these through and it’s clear that each of them evokes a slightly different picture, first of the person speaking (is she calm, or distraught, or out of her mind crazy?) and second of the way she delivers her dialog. If you’re going for a comedic effect, timing is everything.
I’m not saying you should write twenty possible versions of every piece of dialog, but it is good to experiment now and then. And dump the adverbs.