Pitfall #1: The Expository Lump
“As You Know, George,
the Space Station’s Orbit Is Degrading Rapidly,
and We’re Running Out of Air.”
Every sf story contains information that the reader must know. Getting that information across gracefully is difficult, but rewarding. Handing it to the reader in the narrative can be done carefully. Handing it to the reader in a lump of expository dialogue is generally not graceful.
Detection trick: If the phrase “As you know,” or “As you should know” would make sense in a line of dialogue, the dialogue is probably an expository lump.
Under no circumstances (except for broad humor) should you insert the phrase “As you know” into a line of dialogue, even if it would make sense. Especially if it would make sense! If the only way to get information to the reader (after you’ve sweated trying to get it in some other way) is by having one character tell it to another who already knows it, for heaven’s sake don’t draw attention to the fact by adding “as you know.”
Useful technique: It’s easier to describe something if it’s broken. If something is broken, then you notice it. If it’s working right, it just sits there being invisible doing its job. Not to be overused!