Yes, it is that time again! Another lesson from the book of Snarktacus! :) Sit down and buckle your seat belts. We're in for a bumpy ride.
At the start of the book, the chapter, the scene--give us action. Don't give elaborate descriptions until the reader is hooked by what is going on...then you can describe. Tell us what is happening and why we care, then tell us what color their hair is. etc.
Using "looked like" or simile, takes a reader out of the narrative. It makes someone else interpret for you what they are seeing. Using "was" or metaphor pulls them right in and describes what the reader is seeing, instead of the intermediary. This is particularly important in first person POV.
The first step for great writing is imagining deeply. Put yourself in the story and drag it around you, smell it, feel it, taste it, and make sure the reader is pulled in with you.
Characters reading e-mail or letters is in general uninteresting. Don't use this in the first 1/4 of your book, or at least show us what it says by reactions and not by just pasting it in the book.
Everything doesn't have to be explained fully--particularly people. Unless the characters eye color is integral to the plot, it doesn't have to be mentioned--particularly not right off the bat.
The only reason to ever have your characters sitting around doing "nothing" is to make the reader and everyone else feel the underlying tension. If that tension is absent, then the scene is pointless.
In regards to over-writing, try not to repeat yourself. If you have already made the point in one way, resist the urge to further clarify with another statement. Trust your readers and they will trust you.
When your MC has relentless action pushing them forward they aren't paying attention to much except what's going on. Don't put in things that you wouldn't notice at that moment if it were you in that exact situation. (the color of the drapes or whatever)
If you remove your reader from the action and the characters with over-writing, you will fail to grab their attention.
Sentences starting with "when" or "after" or "even so" can pull the reader out of the action because it usually doesn't put you in the moment. Likewise, starting sentences with "but" and "so" can be really awkward. Make sure it is absolutely necessary before doing it.
Building the emotional connection with your character is almost as important as building the story itself.
Phrases like "by the way/did I tell you/so it began/etc." in narration break the 4th wall and jerk the reader right out of the narrative.
That's it for today. I hope you learned as much as I did. :)