A long time ago, in a post far away, Sara, a reader of this blog (at least back then she was; I don’t know whether she still is), asked in a post comment:
“Do you have any ideas about how to incorporate backstory and the character’s thoughts into the story without interrupting the flow?”
Accomplishing this is actually much like incorporating any other description into the story, and there are several things you can do.
Forget about it. That is, forget about focusing on the backstory, or internal monologue, or description of the surrounding trees, or whatever has you in a bind. Rather, make the backstory part of your character, and then just tell your character’s story. Chances are, the backstory will come out by itself, at least those parts that are important.
Make it relevant. And by relevant, I mean “relevant to the conflict.” The story conflict is the engine that keeps the story moving forward, so whatever part of the character’s backstory (or thoughts or description) affects the conflict, that part will actually keep the story moving forward. A favorite example of this is the first chapter of Holly Lisle’s Hunting the Corrigan’s Blood, as she describes the setting Cadence Drake finds herself in.
Make it part of the conversation. So the realizations, reflections, and thoughts of your viewpoint character actually serve as one side of a conversation. This is what I did with my character Clydene’s thoughts during an emotionally intense conversation scene. (Note that this scene actually has two conversations going on simultaneously: that between Ted and Michael, and that between Ted-Michael and Clydene’s inner monologue.) Obviously, the other person in the conversation won’t be able to hear those thoughts (at least not normally), but you can still sometimes make it a conversation. In fact, the other “person” doesn’t even need to be a person at all. Imagine a character responding to her lap cat, or to the beauty of the scene around her.
Make it part of the action. Include each descriptive point as late as you can in the narrative, as close as possible to the action that actually requires that description. For example, the way Robert Heinlein described the battle in the lunar warrens, in The Moon is a Harsh Mistress. (p. 311: To read it, go to the above link, and “Search inside this book” for the words “Charged north in Ring corridor.”) Here, Heinlein includes both description of the setting as well as internal monologue of the viewpoint character. Despite this, the action never slows as the Lunar Defense Minister enters the battle to defend his home against the invaders from Earth.
Use the ping-pong. This is actually a generalization of the two tips above. When I say “ping-pong,” I mean what is usually referred to as an “MRU,” a motivation-response unit. (Randy Ingermanson had a good series on MRU’s on his blog.) I like the term ping-pong better. The idea, in brief, is that something happens to the character or that the character can sense, and then the character responds. Repeat until finished. Both action and dialogue sequences work best in this format. In general, if you have a slow sequence that’s hanging up the story, try rewriting it in ping-pong form; that’s bound to spice it up and make it move.