Tip #5
Character Development

Authors like Ally Carter have a website where they have tips on how to create a succeful story. One of her tips are, 'don't put a character if they're not important to the storyline.' (I switched her words a bit.)
Also, expand on the characters. Don't make their descriptions long but describe them by background, subtle hints throughout the story about their appearance. Don't do this:
There is Mathew. A fair skinned brunet (that's the term for a male with brown hair. Brunette is for female references.) with broad shoulders and olive green eyes. Beside him is Sarah. A blonde girl with blue eyes and hair that's up to her shoulders.
Don't continue on with descriptions like this. I've realized over time it is not right. But I've also realized that having not enough description is just as bad. Go ahead and describe like this:
I flip my thick black hair away from my face in order to put on my blue contacts. I then pick up my 001 Maybelline foundation to hide my acne.
You've just implied that the character has fair skin. You also described her very well by writing thick black hair and 001 Maybelline foundation.