Some helpful advice from Bertrand Russell, The History of Western Philosophy (London: Routledge Classics, 2004).

In studying a philosopher, the right attitude is neither reverence nor contempt, but first a kind of hypothetical sympathy, until it is possible to know what it feels like to believe in his theories, and only then a revival of the critical attitude, which should resemble, as far as possible, the state of mind of a person abandoning opinions which he has hitherto held.  Contempt interferes with the first part of this process, and reverence with the second.  […]  This exercise of historical and psychological imagination at once enlarges the scope of our thinking, and helps us to realize how foolish many of our own cherished prejudices will seem to an age which has a different temper of mind. (p. 47)