This is quite a big topic, so I will try to give you some brief examples, then provide you with links to some great sources here on eNotes that will help a lot.
Bronte uses symbolism quite a bit in her novel, and it can often be found in the mysteries and gloomy nature of the moors. The wind, the haunting howling of it, the vast emptiness, are all symbols and tools that Bronte uses to create mood, suggest alienation and loneliness of key characters, and indicate the emptiness of a life without love. That is just one of many symbols that can be found in the novel.
Themes of love, alienation, morality, marriage, family, friends, insecurity and low self-esteem can all be found in this novel. Discussing each one can take up quite a bit of length in an essay, to make sure you pick one well that fits along with whatever symbols you want to discuss. For example, if you discuss how the moors are a symbol of alienation, then you can tie that in to the theme also by saying, "A major theme in the novel is alienation, and this is often symoblized through the moors."
Bronte does an excellent job with characterization, especially in the main character, Jane. We get in-depth looks into her childhood and key events that occurred that shaped her into who she was as an adult. That background plays a key role in most of her decisions, and Bronte reflects that well. Mr. Rochester is an enigmatic character struggling with a deep conflict, and that conflict is shown well, even if we don't know the source of it for quite a while. The contrast between Rochester and St. John is also stark, serving to highlight each character even more.
I hope that those thoughts help to get you started; take a look at the link below also--it will be useful. Good luck!