Reference last season's sale.
Not all sample sales are built the same. Some are open to the public or are VIP events, some carry multiple sizes while others house only their sample size. Don't be surprised if you are forced to wait outside for hours before you can actually peruse the sale.
One important thing to remember is that price points vary. Markdowns can go as high as 80%, but that is very rarely across the board. If you research the sample sale of the previous season, you can figure out how early you should get there, how long you have to wait, and how much you might spend. Information is not always set in stone, but it will help you gauge what you're getting yourself into.