The most important thing in CS: GO is sound, which gives away all of the key information about the enemies. Everything from their positions, movements, utilities used, and weapons used can be determined simply by hearing all of the audio cues that are made throughout the game.
Begin by identifying sounds and attempting to distinguish them. This is critical for breaking down what your opponent is doing, making it easier for your team to win the round. This may necessitate the use of a high-quality headset as well as some audio tweaks both in-game and on the system, but the effort is well worth it.