Not sure if this'll help you, but my squad leader at USNASS gave us some advice that personally works pretty well for me. For the push ups, pump out as many as possible before you start to realize your arms are tired. Then, start pumping them out by tens, fives, or whatever increments you can handle. If you're at 45, just focus on getting to 50. At 50, push yourself and think, just 3 more. When my arms start getting really tired, I also like to widen my arms a little bit to use slightly different muscles. Furthermore, I find that arching my back up (or maybe you prefer bowing your back down--both are allowed in the CFA as long as all four contact points are still on the ground and you resume the proper position afterwards) to rest for a moment helps relieve some of the weight, and then I start pushing again. However, for sit ups, I was advised to keep moving steadily throughout the 2 minutes and don't stop. Fold your arms, grab the collar of your shirt, and don't let go. Make sure that you're moving up and down as efficiently as possible. If you're not already doing so, try to max out your push ups/sit ups everyday, but make sure to rest the days before you actually do your testing. Another candidate at USNASS told me that when he practices, he doesn't start counting push ups until he's tired if you're that hardcore! Good luck!