Be nimble. Everyday I do my research on the symbols I'm trading and the fundamental news that's driving them. I might be trading a large cap that's gapping up with a beat on EPS and revenue and positive guidance. But if I see that stock pop up and fail miserably on the open amidst huge selling pressure, and I look and see the broader market tanking, guess what, I'm getting short, and that's just day trading. The movement of the market, on an intraday timeframe, doesn't have to make logical sense.