I'd like to make a small contribution, as there seems to be no advice on dialogue.
These tips were from some place I have forgotten but I they've been useful.
"A-B" dialogue is the enemy.
"How are you?" "Good." "Wanna have sex?" "No." Dialogue which is predictable, ho-hum, and consists only of simple setups and straightforward payoffs, are much more frequent in game dialogue than it oughtta be. It sucks.
Interrupting dialogue
When characters interrupt each other, the normal (boring) flow of tne conversation is suddenly thrown out of whack and the viewer becomes more interested.
Answer a question with a question
"Why are you such an asshole? "Why are you still talking to me?" Answering questions with questions changes dialogue direction and forces the character who asked the first question to respond in a personally evocative way, without falling into A-B routine.
Avoid cliches with bit players
Just because they have one line doesn't mean they shouldn't be interesting in their own ways.
"Own track"
When two characters are having a conversation and one is ignoring the other while talking about their own thing, they are on their "own track." This is initially confusing to hear, but says a lot about both characters and through its unusual nature makes the dialogue more fun to hear.
Tangent
People talk in tangents, so your characters should talk in tangents too to avoid sounding like expository robots.
Drop first word
Don't have a character say, "are you going to the mall?" Make them say, "going to the mall?" Again, this is how people talk.
Sentence fragment
People don't. You know. Talk in complete sentences.
Delayed answer
Have one character ask a question which isn't answered until much later in the conversation.
Leave the topic and later come back to it
Pretty much the same thing as delayed answer, but with a larger discussion topic. To illustrate this technique, Freeman pointed out a scene from Rocky where two characters begin talking about a slut Rocky used to know, then they talk about a cigarette, then they go back to talking about the girl. "This is your basic slut-cig-slut conversation," Freeman said.
Starts again
If I'm trying to -- if I want to say something to you, I'll probably screw up part of the sentence and I'll try...I'll essentially start the sentence over but rephrased.
Response implies answer
"Hey Anthony, are you awesome?" "Well, you're reading what I'm typing, aren't you?" I didn't technically answer your question, but from my response you can infer how I might have answered if I'd chosen to do so directly.
External interruptions and subtext
If I want to say something to you but I accidentally say the word "bonesaw"
I'll also like to contest the issue of dealing with Writer's Block. I've taken this tip from my English teacher to heart.
Writer's Block does not exist.
It is all in your mind. Your mind discourages from writing usually due to the daunting scope of what you're doing, lack of motivation or lack of inspiration. The most effective way you deal with it is to just start writing. It doesn't matter if it's good or bad, you can always come back later to fix it, you'll have to proofread later anyway. Just start with a simple sentence. Go on from there, connecting the sentences as you go with a central idea to form the paragraph. Using that paragraph, go on to the next idea that would logically follow. Slowly you'll start shifting in to a writing mood and the words will flow out naturally. This works for non-fiction articles to analytical essays to speculative fiction, basically everything that you will mostly likely encounter as a writer.
The only thing I will warn against is when you're stuck in the middle of writing some fiction and you try to continue despite being bored of it. In that case, I suggest you put down whatever you're using to write and go do something else. Nothing good ever comes from being bored with your own writing.
Hope this helps.