I studied really hard before I took the GMAT the first time. I bought the books, did lots of practice tests, I put in the time. I hoped I'd get a good score and only have to take it once. Unfortunately, I didn't do as well as I had hoped.

So I spent a few more months studying, taking more practice tests, taking the BYU GMAT prep course. When I took it again I improved by 70 points. When I looked back on what I thought did the most to prepare me for the improvement I got the second time around, I attribute most of it to just having taking it once already.

(Side note - it was similar for the admissions interviews. I did plenty of mock interviews and interview prep before my first one, but the second one was much better than the first. It just helps to go through the "real experience" more than once).