I have read in various places that a huge percentage of novels should be made up of dialogue, but don't really know how to get it in there right. I don't want them to go off track and start bleating random thoughts or descriptions of the setting. But I want my story to be very dialogue based, supplying the reader with the information they need, without the characters acting in a way that they wouldn't in real life. Any help? Thanks!
I don't think that's true that novels have to be mainly made up of dialogue. I'm currently reading a John Grisham novel and it's probably only 20% dialogue.
Wandering off on a tangent is my favourite part, both when I do it and as a reader of someone else's work. Dialogue can't follow human speech exactly as it is usually so fragmented, but if you don't copy some of the oddities, it becomes mechanical and predictable. Letting them wander off a little is brave, but usually turns out to have a point. In my book my characters do just sit down and have a quite whimsical conversation about the scenery, but what they are really discussing is why both of them chose to be lonely. It's central to the plot but I didn't know that when I started writing it. In my view, tangents are good!
I also find that reading drama or listening to plays on the radio is extremely valuable when it comes to developing a good "ear" for dialogue. Reading plays is also an excellent way to discover how well a story can be told through dialogue alone.
Visit the BBC Writers Room. You can download scripts there from radio and T.V.
http://www.bbc.co.uk/writersroom/scripts/
Well worth a read.