Not writing code until it was _absolutely_ needed would have saved literally months of my working life, and I haven't been working all that long. Business requirements change constantly, so what you think will be needed probably won't be by the time you ship the code.

Continuously refactor your code to remove duplication (See Don't Repeat Yourself / DRY). If you find yourself copying and pasting boilerplate code over and over, it's probably time to refactor, otherwise you find one bug and have to fix it 20 times. Good testing helps you to refactor fearlessly because the tests will tell you if you screw up.

Whatever happens you'll always cringe reading old code - but see the positive, it just shows that learning is a continuous process and that you are now older and hopefully wiser than you once were.

One thing that's been on my mind lately is an old article by Joel Spolsky [1] about accurate estimating. I'm absolutely terrible at estimating but I'm using Joel's method to improve that. Better estimates mean better code. Why? Because if you estimate 1 day for a task that really takes 2 days, you'll be rushing, stressed and tempted to cut corners by the start of day 2. If you've planned 2 days for it, you can use the time more effectively.

[1] http://www.joelonsoftware.com/items/2007/10/26.html