The single best way to understand the bid/ask order flow is to spend a year or so watching it. Try to stay in the market all day long just by watching the time and sales and the DOM, on SIM of course.
Also, along with the DOM, A 2 min chart, throw up a 2 range chart on top of the 2 min chart. As Xelaar pointed out its a great way to,look inside the bars.
This way you'll see a couple of hundred lots hit the bid on CL, yet it doesn't move even though it's showing 20....