I include a little bit of myself in every character I design. Every character always has at least one good trait of mine, and one bad trait. However, the negative traits are usually greatly exaggerated unless I'm in an advanced RP and am able to be more subtle.

For example:
[hider=Anthony] 
Positive- Believes his mind is his greatest weapon/ tool. Extremely passionate about his beliefs. Extremely hard to intimidate.
Negative- Believes his craftiness and intelligence makes him superior to others. Manipulative. Argues for the sake of arguing[/hider]

[hider=Ben]
Positive- Believes in efficient justice. Tries to be friendly. 
Negative- Wary of people who have wronged him in the past. Reckless.
[/hider]
 
[hider=John]
Positive- Helps everyone he can, even if it places himself in risk. Active.
Negative- Sarcastic sense of humor. Mocks those with less experience than him. (This just goes with the jock persona, not a trait of mine). Looks for reasons to fight.[/hider]