I came across an interesting website: http://www.mentaltoughness.me/
It has several areas of discussion and is very much worthy of a visit. One of the topics was concentration and the site listed some of these as concentration keys:
Practice Fatigue
If an athlete tends to lose focus when he is fatigued, he should arrange his practices so that he is fatigued. Then he must practice concentrating while being fatigued. If an athlete does not like being watched, he should practice while people watch. Most of all, athletes should approach practice as if it were the real thing. The game face should not be reserved for game day only. Every time an athlete goes out onto the court, field, or ice she should go out there focused and ready to perform.
Practice Distraction
Practice with distractions surrounding you, and acclimate yourself in ignoring them. Fixating on external factors outside of your control (weather conditions, poor warm-up, or mistakes from prior contests) will disrupt your concentration coming into the contest at hand. Negative thoughts cost energy, creates anxiety, and serves as a distraction to your teammates.
Use pre-performance routines
These can be very subtle or extremely elaborate. Routines help increase concentration and focus because they help block out both internal and external distractions. The consistency a routine provides also helps the athlete perform consistently.
Use cues and triggers
These are effective tools in improving the ability to concentrate. Cues that are task-related help the athlete focus on exactly what they are doing and keep them in the present. For example, a tennis player having trouble with her forehand might use the cue "follow through" to get back on track.
Use key words
Come up with a few key words to remind you on what you should be focusing on during the competition. These key words should also help with your visualization of the event as well. Visualization is one of the best training mechanisms to bring your mind and body together, and also helps you to focus on your everyday cares in your non-athletic life.
Label
Label what your doing 'thinking' just as prescribed in meditation. Don't judge yourself. Don't be angry to yourself for losing concentration. Just label what you're doing 'thinking' and gently bring yourself back to the here and now. Catching yourself doing this by labeling without judging will decrease the amount of times you lose focus and the length.