If you want faster results with pushups, start weight training. If you already are, be more intensive with it. You can increase numbers by either increasing endurance, or increasing strength. For many people increasing pushups is difficult.
Before I got serious about lifting, I could only do 50 pushups on my APFT. Right now I could max out the APFT pushups, and I've been out for 6 years. When I was in, no matter how much I did pushups for PT, I just couldn't get my numbers out of the 50s. Now I realize that my issue was outright strength, which I lacked at the time.