Two words: peer review

Of course, coming back to your own code a few weeks or months later is good, too. Personally, my Perl coding ability is always improving. I might look at the code I wrote six months ago and say, "Jeez, this really sucks," and make it better.

Otherwise, I'm not quite sure if there's a lot you can do in the process of coding. One possibility might be benchmarking but that won't always fix "over coding" as you describe it.