Dialogue
I'm not sure the how-to books aren't correct in saying dialogue is something you are or are not good at. A tin ear for dialogue is something I'm not sure I've ever seen corrected.
I don't think this means dialogue writing can't be improved, but it is the one part of writing that I don't believe can be taught. Having said that, there are some things I've always tried to keep in mind when writing dialogue.
1. Dialogue sometimes means writing sentences exactly the way real people talk, and sometimes means just mimicking the way real people talk. Some people do speak in complete sentences and complete thoughts. Many people do not clutter up their speech with unnecessary jibber-jabber and sounds. No two real people speak exactly the same, and generalities can get you in trouble.
Because of this, no two characters should have exactly the same speech patterns, either.
2. Never put words into a character's mouth. A good character is who and what he is. A good character is the way he is. When he has something to say, let him say it in his way. When he doesn't have anything to say, let him be silent.
3. Along these same lines, never write a line of dialogue just because it's been two or three or five pages since the last line, and you believe it's time to include more.
4. Dialogue is much more than the words being spoken. Good dialogue is about rhythm and cadence and pauses.
5. Reading dialogue aloud is a good idea, but it won't in any way tell you whether or not the dialogue is good or bad, and can't possibly tell you whether or not the dialogue is needed, or whether it holds true for a specific character.
What reading aloud can tell you is whether or not you can actually speak the dialogue without stumbling, whether or not it rolls off your tongue.
But what rolls off your tongue may tongue-tie a character in another situation or with less confidence, and what makes you tongue-tied may roll easily off the tongue of a character who is confident, educated, charming, and erudite.
So decide based on the character, not on your own reading/speaking ability.
6. Examine why the dialogue is there. What does it do? Contrary to another popular "rule," all dialogue does not have to be there just to move the story forward. If this is all dialogue does, the story isn't going to be terribly realistic. Dialogue is also a very good way to reveal character, and dialogue is also good for verisimilitude.
If a situation arises where a real person would absolutely say something, then the character should say something as well. And he will, if you don't stifle him with rules.
At any rate, dialogue is written with the ear, not with the eye, and not with the mouth. Dialogue can't be written to specific rules because no two characters are the same, and no two stories are the same.
For me, the only real "rule" I try to follow is to let the characters be who they are. Let them write the dialogue.