* Don't introduce too many characters in a single scene, especially in the first and second chapter, but not a good idea anywhere. The reader can't keep track. Beginners tend to introduce too many characters in the first chapter.
* Once you've introduced a secondary character, make sure that character reappears at certain intervals, otherwise reader will forget who he is. And if he disappears for long chunks, is he really that important?
* Mix it up. We tend to skim names when we read, so make sure character names vary. Make sure they don't sound or look alike, and don't start with same letter.
* Don't stick two stories together. You know what I mean. You've written 150 pages of one story, get sick of it, think of another plot, but don't want to waste those 150 pages so you just stick the two together and do a little sanding at the seam. I've seen this A LOT. You aren't fooling anybody.
* try to get rid of words like:
Watch out for the words was and been. This can sometimes indicate weak writing, but not always.
* Easy on italics. Apparently some people don't mind italics, because I sometimes pick up books that contain whole chapters of it. I won't read these books, and I wonder how many other readers feel the same. I would say no more than a page or two at a time. Different formatting can sometimes be substituted for italics, such as a block of text with wider margins and condensed spacing. To me, that says this is just as important as the other text.