Yep, I second that on the buy / sell signals. If you are wondering whether to buy a stock and you see a pile of MM's on the bid, and only 1 MM on the current ask, then DON'T put your order on the bid because it is very unlikely you'll get any (you'll be at the "back of the line" so to speak). That is when you buy that ask before it upticks :-)
Great advice!
I also like buying dips, or buying stocks that are falling in price so that I can be in for the bounce. L2 is VERY helpful in that regard. By watching the bid closely, you can see where MM's are piling up, waiting for the price to get down to their bid. Usually it is best to look for that block of MM's because if they have anything to do with it, that's where the price is headed so they can get their cheapies. I'll usually set my buy just one tick above that block of MM's who are waiting at the bottom like a swarm of sharks...just to make sure a get a few shares before the feeding frenzy :-)
News 
Market Data 
Discover 
AI
