LOL - usually never enough. Here's an exercise. Pick up a book, the closest one to you...randomly. Great. That book, without opening it tells you a lot about the book already. How much the author put into it. It also tells you, by holding it, how much of a commitment it will require of you. Now open the book, and look at the blocks of paragraphs. This also tells you a lot, without reading a word. If there's a lot of white space, you know it's easy - lots of dialogue, etc. If there's a lot of descriptive and narative, it will tend to have a more blocked and "tighter" look to it. So it really depends on what type of book you want to put out there. With my writing, I tend to err on the side of description/narration...not enough dailogue. All this to say (sorry, had WAY too much Starbucks today), tell your story. Story should come first. As you do, you'll figure out where scenes go, and where they should be left to the narrative. You can always add more scenes afterwards, in re-write. Edited to add: You'll know when there's too much dialogue in a conversation. It runs dry, and it doesn't add anything to your story. Push the story. If it's not telling the story or adding to your characters (showing, not telling) then there's too much.