You can mute sounds when you're getting the notification by long pressing the Volume Down button (i.e. you're getting a call, you can mute the incoming ring by doing this). Note that this will not set the phone to Silent Mode or Vibrate and will only work while getting an incoming notification.
You could also swipe down on the notification bar (Unless you specify that it won't, it's usually accessible even from the lockscreen) and hit the Sound button to switch to Vibrate or Silent.