I used to do 300 push ups a night -- 3 sets of 100. I followed your link but didn't bother reading the whole thing.
I simply started out doing as many as I could manage, then 3 sets of whatever that number was -- think it was 10 or 12. I ket doing this amount until I felt like I wasn't getting much return, and then I would increase the number by 5. In very little time I was up to 3 sets of 100 in about 30 minutes.
After a while though, my wrists would start to hurt and I would stop for a while. Then I'd start up again and work my way back up to 100 per set for 3 sets.
After doing sets of 100, after a while I wouldn't even start to feel anything until I got to about 80 or 90 in my second set.
It's not really hard, you just slowly but steadily work your way up there.