How so? Simple.
He stood up. She sat down. They glanced over at the desk. He nodded his head.
In just those four sentences are FIVE useless words which need to be removed -- hence, word count drop!
Let me explain...
When you stand -- normally you stand UP. Only a military command to stand down would make logical sense. So when you state "He stood." your character would stand UP, therefore it isn't necessary to state UP.
The same holds true for sat down. When was the last time you sat up -- again, unless you were in a disciplinary or military type situation where they expect you to sit up with a straight back, to state it is unnecessary. So, therefore the "She sat down." can be cut to just "she sat" to make it easier for you and the reader.
The next one is a sly one for me. I see action and therefore I would 'glance over at' whatever but in reality, a person glances at. The "over" is superfluous. Get rid of it. Forget the word "over" is in your dictionary.
And finally the last one. Oooh, a sneaky one, too. "He nodded his head." If he nodded, it would be his head. You don't nod somebody else's head. At this moment, let me slip another pet-peeve of mine for editing. "I like this," she thought to herself. Really? (Yes, I'm being snide!) How often do you think to somebody else? So it would be "she thought." with the "to herself" as a given. Each of these edits remove an extra TWO words from your word count every time you use them.
I did those edits on a 76k WIP -- and lost almost 3k words. It was a bit unnerving but when I evaluated (I was going to say stood back... but again...) the revised sentences were stronger and read much better.
Be sure to read my "That•As•Ing•Ly" tip for more great edit tricks.