Don't focus on that bass drum beating in your head about 160 times a minute. Don't even focus on the dart in your hand, the shaking may throw you off. Don't even think about winning or losing. The only thing that you focus on is the intended target. Don't make it even harder by dividing your focus on other distractions.
Confidence is also a key element in dealing with pressure.
Confidence, quite simply, is convincing yourself that you can hit the target you are aiming at. The thoughts of missing do not enter your mind. It doesn't matter to you what situation that you are currently in. The size of the double, triple, or bull in the finals is exactly the same as it was way back in the first round of the tournament. To my knowledge, I don't think there is a dart board out there that shrinks in size as the night goes on, but, I will have to admit, it seems like it does.