The most important thing you can do is start saving now. If your account increases from investing properly, the impact of growth over time can make a huge impact due to compounding interest. As an example of the difference compounding interest and timing can make, Mary saves $150/month and is 25 years old and Marco saves $300/month and is 45. Assuming an annual tax-deferred rate of return of 6.00% compounded monthly, both Mary and Marco retire at age 65, and the difference in their savings is $150,851, despite having contributed the same total amount of $72,000 to their 401(k).
Marco saved as much as Mary, but because he saved over less time, his money didn't have time to compound and grow as much as Mary's. Start saving as young as you can to maximize your retirement nest egg. If you can't save a lot now, increase your deferral percentage at least 1% more annually. Even if you don't have many working years until you retire, save now, something is always better than nothing. It will at least be a retirement emergency fund, if at times social security isn't enough.