Handling distractions
The most common application of concentration skills is handling distractions. There are three basic steps to overcoming distractions:
Prepare in advance
'Tune in' to the venue on the day
Use  concentration techniques to overcome remaining intrusions

Unexpected problems - of any kind - reduce concentration and confidence a lot. A bit of preparation can make all the difference. (This is realy just a part of good competition preparation, but it's here because it fits!)
Find out all you can For the big events, gather every snippet of information you can, so you know what to expect. What does the field look like? Got a picture? Where's the sun going to be? Where's the Gotcha? (there's always one... like the indoor cycle track at a University Indoor shoot I went to, where the cyclists were whistle controlled, and we had to ignore the whistles and use horn control for shooting...!). Is there a crowd?
Write a 'worst case' list What could disturb you? Bad judge calls? Competitor jibes? Team mates (!?) Write it all down
Use visualisation Roy Matthews' method (right) is a great example. But you can also just sit and think through how you will handle all the things on your list, feeling how it will affect you and working through your response.
Use practice If it'll be crowded, practice shooting snuggled up against some mates (could be fun...). If it'll be noisy, practice with your Ghetto Blaster up full right behind you. If you're worried about jibes, get your mates to stand behind you and snigger while you practice. Get your coach to call some cutters low, or 'time you out' unfairly, just so you can work out how to cope.

With that done, you'll have a plan for a lot of what will hit you. Next step is to fine-tune on the day, and for that.....

 Tune in to the place
The sporting bodymind has a good line on 'attunement'. The principle is simply to take a good look around and get the feel of the place, so you're not surprised later. For a more systematic approach, check the  mental warm-up page for detail on attunement
 Remaining distractions
Finally, for the remaining distractions, refer back to the basic concentration techniques on the Concentration page, to get some strategies for keeping your focus.
Psych Home
Quotable quote
Another leaf from Roy Matthews' book, Archery in Earnest:
"..It saves a lot of stress if you have a general knowledge of the layout of the field .... When I travelled overseas to shoot for Britain, I always read as much as i could about the country in which the Championships were to be held; about the town, about the food, the weather, the history, so that very little surprised me when I got there."
Roy Matthews, MBE, was a long-time British Champion, Master and Grand Master Bowman, and was still making international scores well into his sixties.
Visualisation in practice
Matthews is also reported to use visualisation in pre-shoot practice, on the following principle:

 Go down to your practice field, and start shooting at a comfortable distance
 When you've settled into a rhythm, start visualising the competition venue.. put in the background; hear the sounds of the competition and the spectators; feel the sun and the breeze... Carry on shooting to your established rhythm, reinforcing the visualisation at every shot, so that when you get to the shoot, every arrow is familiar and in context.