JWTroemner.com

If you want the basics of punctuation, check out these guys here:

Mr. Clements.com

Bubblecow.net

Fanfic.TheForce.net

A step past the basics

1) Avoid using synonyms for said/asked, unless that synonym dramatically changes the meaning of the sentence. 

2) British English uses single quotes (‘You’re a wizard, Harry!’) while American English uses double quotes: (“I can show you the world.”)

3) Change lines any time you’re drawing attention to a different character. No, seriously, read that post. Leigh Michaels has some incredible tips for paragraph breaks and dialogue.

Tags and Beats

A dialogue tag is a a label which tells the reader exactly who said what: he said, she said, I said, the borg collective said as one— etc.

• The most common format for a dialogue tag is exactly what I wrote above: [Speaker] said/ [Speaker] asked. The name of the speaker first, followed by the manner in which the quotation is being expressed.
• In times of old, it was common to put said at the beginning of the tag: said Billy, asked the waitress. This order still shows up sometimes, but for the most part it’s considered archaic.
• The most effective time to use the older style is when the description of the subject gets overly long, and the verb is in danger of getting lost. For example:
  “Want fries with that?” the waitress who brought them their menus asked.
  vs.
  “Want fries with that?” asked the waitress who brought them their menus.

A dialogue beat is an action that identifies the speaker.

• The beat shares the same line as the dialogue. This is why it’s so important to switch paragraphs when a person besides the speaker is doing anything. For example:
  “What, is there something on my face?” I wiped my chin.
  He pointed at his own cheek. “Right over there.” 
• Beats tend to be short. When they get too long, the reader can start losing track of what’s actually said.
• In the same vein, using too many beats in one conversation can become distracting, and draw attention away from the dialogue.
• Keep the actions important and relevant.

And sometimes, your best bet is to use nothing at all.

• This works best when you’ve got only two characters with distinct dialogue.
• Use it alongside beats and tags.

All used together, it looks something like this (tags will be in bold, and beats in italics):

“Could you please move?”
“It’s a possibility,” he said. “Who’s asking?”
“The person whose rib cage you’re crushing. If you could just— thank you.” I rolled over and took a breath. “I have to say, I’m a little bit disappointed.”
“Disappointed?” His eyes widened. “I’ve been doing this a long time, mouse. Nobody’s ever tried to give me a critique.”
“I’m not complaining,” I said quickly. “Not really. I appreciate your being here. I do. But the stories always make death seem so… romantic. This is… not.”
“You can’t be serious.”
“It’s just that you only die once,” I said. “I suppose I expected it to be a big to-do.”
“Then it’s a good thing you’re not dead.”