Know Your Characters as if they were your best friends

This is very important especially when writing fiction or fantasy, since they are the elements that really hold the story together. The worst thing you could do is write about no-personality, flat characters.

Although this is entirely subjective, I find that basing a character on someone who is close to you, i.e: your mother, your sibling, your best friend, is a great way to really add depth to your character, and it makes it easier to imagine what that character would do in the situation given.