The best way to increase pushups, as well as situps and pull ups, is to pyramid your weight. I can't post links yet, but the full article is up at internetgym.smworth.com
To give a brief explanation...body weight exercises can be increased effectively by increasing the volume. Right now you are doing 25 for each set for 200 total reps. If you pyramid the weight it will feel easier, but you will be greatly increasing your volume. If you can do a max of 40 pushups right now, pyramid your reps from just 5 pushups. Increase each set by 5 until you hit 40, then work your way back down to 5. Limit your rest to about 60-90 seconds if you can. And make sure you stretch your chest in between each set.
So your sets will look like this:
5, 10, 15, 20, 25, 30, 35, 40, 35, 30, 25, 20, 15, 10, 5
You will be increasing your sets, reps and volume, as well as finishing 320 pushups. Make sure you don't do this anymore than every other day(mon, wed, fri, with the weekends off). If you know the date of your physical agility test (since you mentioned a 1 min pushup test I am going to assume military or police agility test) make sure you stop doing all pushups 3-4 days before the test to allow your muscles the rest they need.
If you want you can try a 1 set max on Sundays and readjust your numbers if needed for the week. I have been a member of SWAT for 10 years. This program is actually built for the purpose of increasing your max numbers. Good luck!
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