A good thesis must state an opinion, meaning it must be arguable, and it must be specific. For instance, saying "Oedipus Rex is about pride or hubris" is not a good thesis, first, because nobody would argue about that, and second, because is it too general.

However, pride is a good place to start in writing an essay about this play. Oedipus is a very proud man. One way to argue would be to say something like the following: "On the whole, Oedipus's pride works for the common good but also leads to his personal downfall because he is blind to his own shortcomings."

You would then want to find support for your thesis. You could talk about how Oedipus's pride in caring for the well-being of his people works to their advantage: even before they come to petition him for relief from the plague, he has been proactive, sending Creon to get advice from the oracle at Delphi. Oedipus, also, in his opening speeches, expresses his compassion for his people. His pride also keeps him from backing down when he is warned that he should not keep investigating what led to the plague: he is confident he can get to the bottom of it, and that pride in his abilities is what the people need.

Where pride goes wrong is in Oedipus's blindness to the possibility he could be the cause of the plague. If he had listened to the warnings as a hint of his own wrongdoing, he would have been prepared. But he thinks he can do no wrong, and the shock that he can almost destroys him. You could talk about how his having the self-awareness that he might be in the wrong might have allowed him to prepare Jocasta so that she didn't kill herself, and allowed him to prepare so that he wouldn't stab his eyes out. You might conclude that what was good for the people, ending the plague, was bad for him personally.