Some people you could read without having read from the beginning. Nietzsche, Descartes, Sartre. But if you're wanting to tackle guys like Berkeley, Heidegger, Kant or even newer guys like Saul Kripke you're going to want to go back and read Plato and read the guys from the analytic tradition like Bertrand Russle, Frege (even if he was kinda off about his ideas), Leibniz etc. The problem is you're going encounter philosophers who use words like "idealism", "monad" and other words that may or may not seem familiar and often have different meanings than what you're used to them meaning. Reading, or at least having a good understanding of, the works these guys read to come up with those words is important. If you're interested in philosophy I strongly recommend checking out the Partially Examined Life podcast. It's very informal, but very interesting discussions.