Want to get batter at DOD:S?
DoD:s is, at its basis, only pointing and clicking. You find the bad guy, point, and click.
Build your reflex shots and reaction times by using these links:
http://www.humanbenchmark.com/tests/reactiontime/index.php
http://www.missionred.com/games/reflex2.html
http://www.missionred.com/games/reflexte.html
http://www.missionred.com/games/reflex3.html
As mundane and repetitive it seems, these simple tests will build your reaction times if used regularly and will help with your gaming. Trust me, they work.
Enjoy!