I also raised my GPA by I'm not sure how much, a fair bit. I took the MCAT 3 times, so depending which scores you take, I could have gone up 9 points since the first time I took it. But not everywhere does that.
I also did some travelling, but I don't know if that's an "improvement", just something I love doing. I wrote a much better PS, and applied much earlier. Stayed with my previous EC's, but didn't add much new.
I looked at my calculated GPA's on my AMCAS, and you can see a nice positive upward trend as I took more difficult science classes, which is also a plus. My senior year, I had 20 credits of chem and biochem classes, and had around a 3.7 GPA. However, I started off freshman year with a BCPM around 3.3. So I guess it couldn't hurt to see a trend over 4 years instead of 3 years, shows more consistency I guess.