Here are a few possible traits for Winston:
Intelligent: He is good at his job, whether he wants to be or not. He is able to manipulate words to create truth, and does a very good job at it. He is also able to detect the hypocrisy and inconsistencies in the Party's strategies and platforms. He is smart enough to realize he is being manipulated, and that the party is total bunk in most of what it says. He is also smart enough to try to not be detected in thinking these thoughts, or in showing any discontent.
Contemplative: He is a deep thinker, that analyzes things and really plays them out in his mind. He spends quite a bit of time pondering his failed marriage, and why it didn't work. He thinks of his mother and sister all of the time, and wonders what his role was in their disappearance. He thinks constantly about the party and whether there are other people who feel the same way that he does. He analyzes every facial twitch of everyone around him, contemplating whether or not they indicate a similar discontent.
Courageous: When he receives possible information on how to rebel, Winston is willing to give up anything to do it. He bravely risks all to meet O'Brien, and indicates a willingness to fight however he needs to in order to defeat the party. He also is incredibly daring in his meetings with Julia and in securing a room for them. He risks his life every time he meets her.
I hope that helps; good luck!