In my years of evaluating manuscripts, I noticed the most common big mistake in scene openings is a lack of focus that results in confusion. I’ve read a lot of first pages where I’m exhausted just from trying to keep track of the names of nine characters and make sense of the situation, the people, the setting, the action, and the thoughts. Look, the purpose of the first paragraph isn’t to tell everything needed to understand the book. It’s just to get us to read the second paragraph.