If you have done something, and want to lie about it, one of the best ways is to appear to grudgingly accept blame for something you didn't really do. Here's how to do it.
1. Create a basic profile for your character. Don't go too crazy here, write down basic information, such as name, age, job/class, gender, and other simple checklist one-word things.
2. Create goals, treasures, and banes. Everyone you know has a goal, a treasure, and a bane. Frodo's goal is to destroy the ring, his treasures are The Shire and his friends, his Bane is the ring. Keep this very simple.
3. Based on goal, treasure, and bane, create background. This will take time, so start by writing one sentence of each, in separate paragraphs, then develop as you see fit and get ideas.
4. Create idiosyncrasies. These are like habits or compulsions: nervous eating, picking one's nose, phobias, funny rules about eating (for example, always needing to eat the last bite), quoting books constantly; These are things that will help define your character, and make him/her more human.
5. Define what it would take to make your character cry. Crying is the ultimate expression of emotion. Your character doesn't necessarily have to cry, ever. At least on the outside. This helps your audience have empathy for the character.
6. Finish fleshing out the character's flaws. Does your character hate one of the other characters so much that he won't be in the same room? Does your character have a tendency to space out while fighting due to something exciting happening to his left? Flaws are the final, most important trait to realistic characters, as they mark the character as something more than just a 'Mary Sue.'
7. Get to know your character really well. Try pretending your character is sitting in front of you, and have a conversation with them, as a four-year-old child would to an imaginary friend. Be serious. While talking to your character you can discover many important things about them, such as speech mannerisms and the way they think, without forcing it. They will come out of the character naturally, and therefore sound natural when you write.
8. Create the character's appearance, background, and personality. Finish fleshing out your character so that you can take all the notes you have been making and put them into a simpler character sheet.