I've been thinking about pacing in a story and what effects the pace of a story. Here are my thoughts:
Short sentences are fast.
Long sentences with many many adjectives, adverbs, and other additional words can be slower than brown molasses in a cold, wet January to read, so that by the time that you get to the end of the long and convoluted sentence, you've completely lost the thought that the sentence was trying to convey to you and you have to go back and read the sentence again to figure out just what the author was trying to say. Where was I?
Passive versus Active voice
I was writing this blog post reads slower than I wrote this blog post.
A catalogue of descriptors reads slower than descriptors which move and act.
She sat on a soft, blue chair in the living room. The living room was lined with bookshelves. A television, dvd player, and VCR sat on top of one of the bookshelves. The window had sheer curtains. The carpet was brown. The walls were white.
zzzzzzzzzzzzzzz ... yawn ... where was I?
In the living room, she lounged on a soft, blue chair. Books marched with military precision across the shelves lining one white wall. Sheer curtains fluttered in the breeze while the TV, DVD player, and VCR perched precariously on top of the bookshelves. A good stiff wind would knock them to the brown carpet waiting below.
Bah! That was crap, too, but I think you get the picture.
Similar to description, backstory which catalogues past events is slower than backstory which is active in the narrative.
This can be tension between two characters anywhere from a friendly debate between two friends to having Darth Vader and Luke Skywalker in the same room.
Tension can also come from the environment. Dorothy following the yellow brick road is not as tense as Dorothy in the spooky forest. (Though horror writers can follow the butterflies on a bright and sunny day and have the reader hiding under the bed in fright.)
If nothing is happening and there is no hint that something could happen at any moment, then there is no tension. (Previously mentioned horror writers usually have some hint that things are not as it should be while following the butterflies on a bright and sunny day.)
Putting it all together
If you want to speed things up, then use shorter sentences with active verbs, ratchet up the tension, leave the backstory out, and make your descriptors move.
If you want to slow things down, then take the reader on a long and convoluted journey following butterflies on a bright and sunny day while passively cataloguing everything in the environment and the entire backstory of one of the minor characters.
Did I miss anything which effects pacing?