Get under your character's skin
To introduce your character to the reader, you must first introduce them to yourself. Get to know them well before you begin -- this helps with the plot, and is a life-saver for characterization. Remember -- no one in the world will know as much about the character as the author themself.
It helps if you begin with a brainstorm. You don't even need their name. Just decide the gender of your character, and begin writing down anything at all about them.
Delve into their past a bit, look at their parents, their school. Did they get bullied? How does this affect them? Were their parents kind? Cruel? Was your character a rebel or meek and submitting?
Give them a look in the mirror. Write down their looks. Don't bother stopping to say 'Oh, is it boasting to put down...' It's not. And keep in mind that not all of the description will find its way into the book, only in your head.
Personality. What is a character - what is a PERSON, without a personality? Give them something here. Are they funny? Sarcastic? Do they have a spitfire personality, or or they the type to keep quiet and to themselves?
Basically, take your character to tea and learn their life story. Even the best authors do this, and it really does help.
Know them like you know yourself. Because, when it comes down to it, all they are is a part of you.