Depends on your style. I know of several successful traders that only trade from the book (level 2) and the tape. They have price levels marked down that they're interested in and they watch the tape at that price level to see how it acts. If it acts the way they expect, they get in, if not, they wait. Tape reading is an art form and take many many months of experience, probably longer to get good at it.
For me, I don't watch the tape or the book (level 2). Not my style. What's your style? :)