The best way to get a couple of these acheivements (100, 200, 300, 600 test score) is to play a test match (i used England versus Kenya).
Assuming you are familiar with the save option, play very aggressive, using only the B button to loft all shots, and aiming generally away from fielders positioned in the deep. For short balls, go back in your stance (LT) and hit to 2 or 9 o clock, and for full balls, come forward (LB) and hit it straight over the bowlers head. The key to pushing B is just before the ball lands on short balls, and a bit earlier than that for full balls.
After about 10 overs your batsmen will be fearless, and the bowlers timid. I was able to average about 24-30 every over (saving every over), and as such managed to get the 100, 200, 300, 600 achievements in under 2 hours.