Thanks for this post! I have been asking myself the same questions and found the following answers so far:
- In the long run, meditation can help. It has to be done with the same consistency as the training though.
- Where does your train of thought go when your thoughts go crazy? It can be worthwhile to examine it in a quiet moment outside of the competition to find out from which kind of fear they stem. Once you know the fear, you can devise a remedy.
- Try to bring 80%, the adrenaline will take care of the other 30% 
- Remember all the good hard work you did during your training, trust your body, it knows what it has to do.
This is why I love to watch Mr. Storl throw - he very often seems to smile when he gets ready to throw, like he knows exactly what he's doing and that it will go well.
- Bring a friend who believes in you and/or a good luck charm 
Oh, and I can recommend the book "Die Kunst der Höchstleistung" by Alois Kogler, it has some really useful advice regarding mental training techniques.