I agree with being patient. If you aren't too particular about where/when you're going, you can book pretty close to the date. For example, I was able to score roundtrip tickets from NYC to Lima for 35k miles on American and I booked about a month in advance.
However, if you're looking to go to a very popular place during peak season (i.e. U.S to Australia during Christmas), your best bet is to book almost a year in advance or as soon as the airline opens up the space. It really all depends on where you want to go and when.
Whatever you do, though, don't be tempted by offers to 'sell' your miles. In most cases, airlines don't allow it and you can actually have your account shut down and lose all the miles you accumulated if you get caught.