I realize that I use the word “craft” a lot.  What do I mean by that?  Craft is a set rules that can be broken, but not until you’ve mastered those rules.  There are very basic issues of craft –word choice, sentence structure, punctuation..  (Although I will freely admit that I’m baffled by the comma.  I tend to use them as a rest in music, or a pause in delivery as if I were an actor delivering a line.) 
Here are some other examples that are a bit more sophisticated — open a scene in the midst of that scene.  We don’t need “Knock, knock.  Come in” in most instances.   Dramatize dramatic events.  Don’t give me a scene about peeling potatoes.  Show me something exciting.
Controlling the number of view point characters which requires deciding who should be a view point character, which is why I like to outline.  I can find out before I’ve written eight chapters that I don’t really need to have General Snivel’s POV.  There’s the simple issue of controlling view point.  Most of us use the # to indicate a change in POV.  A few writers can/could do it on the fly in the middle of a page.  Georgette Heyer was a master at this. 
Make sure a scene actually advances the plot or at least explicates character.  The real mark of a master is when a scene can do both, but in a subtle way that’s not “on the nose”. 
Use the rule of three to help sell a point.  Differentiate dialogue in other words, make the characters sound different, and that doesn’t mean by doing god awful dialect in prose.
I think flashbacks are very hard to do well.  They often times end up feeling like the writer couldn’t bear not to tell you about this character’s traumatic experience so they give you a flashback.  I’d rather have the characters talk about the traumatic event in the moment.