It depends on my goals.If I just want to learn something,I do a little bit research on the subject and what could be good books on it and tgen head to Amazon or local book store for it. If haven't got a concrete goal and just want to explore some random topics,I again hit Amazon and browse random categories,read some literature reviews by critics in newspapers and etc. Also,reading feeds reading. For instance,I was reading some comments on Financial Times and saw someone making a fairly reasonable argument about queuing theory.Not being familiar with it,I googled it, found some very interesting courses and books. Will do a bit of exploration of this topic in near future.