Worry about the dialog later. GO through and write the story, adding all the necessary bits through the dialog (stuff that moves the story through) and then when you're done, go back through and read the dialog out loud. If you find yourself laughing at something that's not a joke, then you need to change it. Also, keep in mind what period you're writing for. If I were to write a story about the 1950s, then I shouldn't use works like "krunk" and so forth. (That's obvious stuff, but you would be surprised what you'd find...)
Yes, so the best advice I can give you is to write now and revise. I read this thing by Stephen King on writing and he suggest you do this with everything, especially facts. Can't remember something, make a place holder and then fill it in once the story is there.
Sorry if that's not what you're looking for, but I've never really had a problem with dialog. I've had a creative writing teacher tell me I'm a natural at writing dialog.