Try doing them every day for only two weeks. Don't do other pec, tri, delt excercises in that period, because that will be overtraining. I am currently following a daily pushup regimen by the world famous trainer Pavel Tsatsa-how-do-you-spell-it (The Evil Russian). It lasts for two weeks and goes like this:
Intensity Frequency
Mon- 100% (test); 40% 60 min
Tue- 50% 30 min
Wed- 70% 45 min
Thur- 40% 60 min
Fri - 80% 60 min
Sat- 55% 90 min
Sun- 20% 90 min
On monday you do one set of as many push-ups as you cn possibly manage (your max). Then you just follow the template above. For example, if you tested your max to be 50 pushups, then on Tuesday (going by the above template) you would do 25 push-ups (50% of your max intensity) every 30 minutes from the time you eat breakfast till the time you go to bed.
On sunday you would be doing 10 push-ups every hour and a half.
Test your max each monday and adjust your max accordingly.
According to the article by the evil russian (in muscle media magazine), this will greatly improve your gains when you get back to regular training. For one thing, it improves vascularity, which is crucial to muscle growth. Personally, I saw new veins popping out after only 4-5 days on this program, and they just get more noticable the longer i stick to it! I now have veins spreading over my shoulders, pectoral region, and even biceps where i had never seen anything before! I was very impressed. Hope this helps any. Good luck