Firstly go to 2012ticketchecker.com/ this website tracks and tells you when tickets are put up for sale. When you know the event number you want to go to, type it in the website and if and when tickets you want for that event are put up for sale you will get alerted by either an Audio alert or Pop up alert, this afternoon I purchased 6 tickets for the Velodrome.
You don't have to refresh the webpage as it does it automatically, if you have a twitter account follow benmarsh as he set up the website. On the website it tells you what to do and also gives you tips on snagging tickets, the biggest tip I can pass on that helped for me is that If you miss a batch of sales, leave them in your shopping basket and don't close the webpage if or when LOCOG put more tickets on sale you'll be ahead of the pack by already having the tickets in your basket.