You have left this question incredibly open, and so I have included some links below to help you access further information about themes and characters in this excellent novel, which will help you to find out more about some of the key interests. Any of these could be used as a basis for an essay. For example, you might like to write about the theme of class in this novel.
The rigorous scientific conditioning that has produced the "brave, new world" of the novel has successfuly done away with class conflict. The Controllers, in deciding that there should be five social classes from Alphas to Episolons, have therefore created a system where everyone is genetically bred and conditioned to accept their lot in life and be best adapted to their class in life. There is no sense of class envy or a desire to achieve social mobility. Note the way that the Epsilons receive less oxygen to ensure their lower intelligence as the Director of the Hatcheries explains in Chapter One:
Hasn't it occurred to you that an Epsilon embryo must have an Epsilon environment as well as an Epsilon heredity?
Thus it is that embryos that are marked to be Epsilons are given less oxygen to impact their brain.
However, it is clear that in spite of this rigid delineation and how it is accepted, Huxley seems to be satirising the importance of class in British society during the time he was writing. One way he does this is by focusing on how different classes look physically different but how they all wear separate colours to avoid confusion, just as we today wear certain types of clothing to identify us as belonging to a particular social class. Secondly, class is satirised by the introduction of John the Savage into this world, who has not received the same kind of conditioning as others, and thus when he sees a dark-skinned Epsilon, he thinks of Othello, a Shakespearean hero famous for being both dark-skinned and noble. John, unlike the new society around him, does not judge by appearance, and Huxley thus seems to be pointing out the hypocrisy of society in judging by social class rather than judging by looking at individuals and their worth alone.