At first Winston is very scared and not bold enough to rebel. He uses his diary to expresses himself and his thoughts about life and the oppression from the state.
The character of Julia being introduced we think really helps develop Winston's character. Not only does she help him and support him, she makes Winston realize that love is a feeling and that it is okay to feel it.
Slowly, Winston becomes less shy and timid, and becomes independent, bold, and free. We see how his character changes, he even meets new people and debates the idea his has on a non-authoritarian government.