I'm an amateur writer. Whenever I write, I tend to put in too much dialogue and not enough story. What are some techniques I can use to space out my dialogue?
Why do you believe you have too much dialogue? To take the question to an extreme, have you ever read a play? It's all dialogue, and yet plot happens.
Now, I understand you're not trying to write a play. But if your strong point is good dialogues, why not work with it? You can write the dialogue, then add descriptions of how your characters said something, what they did while they were talking, actions, interactions, gestures. What characters were thinking, holding back, not saying. Things might be happening while your characters are talking.
For a brilliant example of what I'm trying to say, read the first chapter of The Master and Margarita. All of it is dialogue between three characters, with very little actually happening. And yet, we are treated to so much...
Of course, your dialogue has to have a reason to be there. If it doesn't serve the plot in any way, it can go. But that is true of any text, not only of dialogue.
If there's "not enough story," that's your primary problem. If the story is solid, how much dialogue to include is a simpler choice. Where did you get the idea that there is not enough story? Reader feedback?
One way to think of dialogue is that it is an action (forget about Tarantino style banter for now). If you are letting the reader know about verbal actions the characters are taking, there should be a reason. If the dialogue isn't part of a dramatic event, it can probably go. If a scene (section of writing) doesn't involve something happening, that scene can probably go.
First develop your plot from start to finish. Divide the story into scenes. Then develop your characters and give them the appropriate dialog at the appropriate moments. This way, no matter how much dialog you write, it won't hinder you from the plot, which you will have already done. Then as you begin to edit your story, delete everything that doesn't advance the plot in some way. If you suffer from logorrhea of dialog, that test will trim it down to size. Remember this fundamental rule of writing: a reader can stop reading at any point.
Ask yourself a basic question: why are my two characters speaking to each other? Chances are, it is for one of the following reasons:
to prove how witty they are (and, by extension, how witty you are as author)
to ask about something
to confirm or deny something
to avert suspicion
to blame or praise someone
to promise or threaten something
to explain something
to deny something
to help someone or frustrate / hinder them
For reasons 2 to 9, you can ask one or more of the following questions of yourself as author:
A. Why are they saying what they are saying?
B. When are they saying it?
C. To whom are they saying it?
D. In what circumstances are they saying it?
E. What are they trying to achieve by saying it?
F. What are they trying to avoid by saying it?
Once you start to ask these questions about your characters and their dialogue, you will see how you can add plot elements. If I'm blaming someone, something happened. What was it? If I am threatening someone, they have done something or might do something or have stumbled upon something ... tell me what it was. Set the context.
Asking yourself who these people are and why they are saying what they do will help you to understand who they are and give them things to do as well as things to say. It will help you to put them into situations. Characters need to be put into situations and then taken out of them again to advance the plot of your story.
As others have said, make sure you have a story! In the real world, people rarely talk without a context and the context in this case is what should inform and drive your plot.
If your dialogue primarily falls into the first category (to show off), then you really need to rethink what you are writing and why. Nothing wrong with showing off: celebrities are forever writing books which show them as intelligent, witty or erudite human beings. However, such books do not fall into the category of fiction as the term is popularly understood although they may be fictional nonetheless.