Iteration, Iteration, Iteration:

Iteration is everything. 

Writing the same code over and over through iteration encourages learning through what you have done and/or done wrong. It always seems (at the time) that I am doing everything in a great or at least reasonable way, however, once I come back to it later I often end up asking, “Why did I do that?” or “What was I thinking?” even though I know what is going on in the code, it's just I know now there is a better/easier way of going about it.