This is quite possibly THE SINGLE. MOST IMPORTANT THING. In your entire application. ANYONE can usually think of using a fire power or some such thing. But RARELY does two characters have the exact same personality.
When creating the personality traits of your character, select one from each of the following personality trait pairings. When you have chosen, you need to describe how they are that, and to what degree are they that?
Following these guidelines will help you piece together a KILLER Personality, but it will also help you roleplay your character. The GOLDEN RULE of Role-Play is to RP the character, not yourself! If you have an insecure, naive, cowardly, pessimistic character, but you (in real life) are courageous and extroverted, you might look to impress other characters or search out missions to accomplish or defeat bad guys or enemies - or even train. YOUR CHARACTER WON'T necessarily be seeking those out.
Personality Traits -
Optimistic or Pessimistic
This describes the way your character views the world and events going on around them. One of many questions you can answer to cover this is if your character sees the glass as half-empty, half-full, or soon-to-be-totally-empty. Going into further detail than that would be much appreciated.
Idealistic or Rational
Does your character follow his heart and ideals, or does your character simply tend to follow the facts?
Imaginative or Logical
Imaginative characters are those who are artistic, asthetic, creative thinkers.
Logical characters tend to see things from a cause/effect, black/white, this/that, or true/false angle.
Playful or Serious
Playful characters are laid back and enjoy themselves and others.
Serious characters prefer to stay focused on their goals, more often than not.
Extrovert or Introvert
Extroverted people prefer to be with other people and can even fel energized by other people's company. Sometimes they might be uncomfortable when it comes to being alone.
Introverts are uncomfortable with other people and often find interacting with them as more of a chore than as a pleasure. Introverts tend to be quiet and withdrawn, preferring to find a quiet place to rest, regroup, and decompress.
Couragous or Cowardly
Couragous characters that can stand up for their goals and ideals even when they are afraid. Characters can also exhibit the quality of staring death in the eye and not flinching. Courageous characters tend to be confident, and are commonly considered heroic - or stupid.
Cowardly characters tend to be concerned with taking care of themselves, by any means required, even at the cost of another's well-being or convenience. They may shy away from any trials or simply be non-confrontational and submissive.
Confident or Insecure
Confident characters are self-assured. They tend to be in touch with themselves, knowing their strengths and their weaknesses. Some characters can be overly confident.
Insecure characters suffer some negative self-efficacy and image, either feeling too weak, or too ugly, ect. They tend to be submissive and non-cronfrontational.
Clever or Naive
Clever characters are capable of seeing through plans and deceptions, and pretty good at making their own as well.
A Naive character is one who is easilly tricked or decieved. This does not necessarily relate to a character's level of intelligence, but this determines how well others can pull one over on the character (Naive), and how well the character can pull one over on others(Clever).
Caring or Cold
A Caring character is one who is given to following what their emotions tell them. They are often empathetic and like to take care of others. They are guided by their feelings more than anything else
Characters who are Cold can still feel emotions, it simply isn't a powerful impact on them. They tend to be driven by another stronger factor.
Organized or Messy
An Organized character prefers to be neat and organized, maintaining a controlled environment. They tend to plan things out as opposed to just winging it.
Messy characters are often slobbish. They tend to prefer circumstances that are scattered and in disarray. Some characters might be in total control despite the mess, other characters might be totally flustered or embarassed.
Other things to consider for Personality:
Refer to your Background Story. Are there any events that influenced your character to becoming what it is to the present? Or is your character still holding on to memories or events in their past? Or do they worry about the future?
Make sure the personality traits make sense in relation to one another in nature AND in degree.
These questions in the above paragraph are why it is important to describe to what degree a character exhibits the aforementioned traits. Events are one of many things that can help you describe those degrees.
If you stick to these ten traits, your personality will be defined well enough that you will be able to decide if the personality is your character's or if it is your own. You do not need to write ten huge paragraphs going over every scenario where they may behave differently, each trait will be capable of explaining whether or not it is possible.