It all starts at the beginning of each round. You know the opposing team starts at its spawn. The primary engagement points lie where the two halves meet. As soon as the round begins, the Ts have the option of going either through the H or through the tunnel to reach the CT side. Also, train yourself to buy your equipment at the beginning of each round quickly, so you're ready to run with your knife out as soon as you're allowed to move.
Slow buyers lose valuable time and allow the enemy to get in better positions.
Stick together You will almost always want to move with your teammates. If you get into a fight, your teammates will help you kill enemies faster, and they'll also give enemies more targets to shoot at besides yourself. If your opponents are all shooting at your teammates, take that free second to do as much damage as you can since all those guns will soon be pointing at you if you don't take them out quickly. Once in a while you may end up with a gung-ho partner that insists on charging out whenever possible. When he makes his move, you have to immediately decide whether or not to go with him.