Effective map reading is a combination of two primary skills, knowing where you are and where the opponent is, and knowing the best places to engage yor opponent.
Even if you know your weapon, know how to aim, and have the initial bead on your opponent, if you choose the wrong spots on the map to engage, you will lose more often than not. You may win the first engagement, but the odds go down for each following one. Most FPS maps have several key points, where you can stop the opponents in a bottleneck. The key is to identify these crucial spots, where you can engage multiple opponents for an extended time.