They do a lottery around the beginning of the year. The actual sale is in late February. If you win the lottery, you can then buy tickets, but you need to log in pretty much as soon as the sale opens.
Alternatively, I am sure you can buy them on stubhub at an appropriately inflated price.
The standing room is a reasonably good deal. Doing the seats once is worth it, but pricey and, frankly, I prefer seats where I can see all the outfield action.