S.P.
I have had amazing "arm de-flabbing" luck with push ups, but you have to do it with your hands very close together to make it work. My spouse taught me this. He was the "one arm push-up" king in high school. He said that the placement of the hands determines the exact muscles used. Make your first fingers and thumbs into a diamond shape in front of you. I guarantee you'll see some improvement.
You also need to know that when I started, I couldn't do TWO push-ups. I can now do 20 on a normal day and sometimes I do two sets! It took several months, and maybe every week, I would try to add two.