Update your resume on a monthly or quarterly basis
It's difficult to look backwards and reflect on all the work you've done. If you've been working at the same place for 3+ years, I suspect you can't remember half the interesting things you've done. While you don't have to actually drag our your resume and make regular updates, you should create a log file of some of the interesting things you've done. Keep regular notes on tools, technologies, new techniques, recognition and awards, conferences/workshops/training, and other accomplishments. When the time comes to actually update your resume, you'll have a wealth of information to look through to help you build different resumes targeted at the opportunities you're interested in.