In philosophy? I would start by reading a few good general historical reviews of Western philosophy. An excellent, lively, and informative one, is by a countryman of yours, Anthony Flew, who is an eminent philosopher in his own right. An Introduction to Western Philosophy. Another, very eminent philosopher (and countryman of yours) is Bertrand Russell. History of Western Philosophy. After that, if you are up to it, you can begin to read primary texts. I would not start with the pre-Socratics. I would begin with the famous early Socratic dialogues by Plato. Apology, Euthyphro, Crito, Phaedo. You can read all of them on the WWW. Just google them.