If you have planted the bomb, your objective completely changes. You no longer need to kill the enemy team; you only need to ensure the bomb explodes. Time is your greatest weapon.
Hiding vs. Peeking: Once the bomb is down, find a safe position where you can hear the bomb being defused. Do not peek looking for kills. If you hear the defuse sound, do not swing out wide. Jiggle-peek the angle (shoulder peek) just enough to force the CT to stop defusing and look at you. Every second they spend aiming at you is a second the bomb ticks closer to detonation.