Pay Yourself First
Set up your savings like a monthly bill that needs to be paid, so that a certain amount is automatically transferred each month or pay period to your savings account. The amount does not have to be large, consistency is the key. You'll never forget a payment again and you'll never be tempted to miss a payment to your savings because you won't even see the money going directly from your paycheck to your savings account.
Increase your contributions consistently
Incrementally increase your savings every year. With compound interest, even a small increase can make a big difference over time. See if you can set up "auto-increase" for your 401(k), if you have one. This allows you to choose the percentage you want to increase your contributions and how often. Doing so eliminates the temptation to avoid setting aside a larger amount.
Invest in the Stock Market
Expose yourself to the stock market by using index funds or ETFs. An index fund is the cheapest and easiest way to diversify the money that you're investing. You just make the investment and the index funds handles the diversification by rebalancing through buying and selling of shares in particular companies. These funds are also a lot more tax efficient compared to trading in and out of stocks. Finally, the management fees are a fraction of what it would be having someone manage a portfolio of stocks.
Forego the "little" expenses
Those little expenses scuh as a Latte or Starbucks coffee, add up over time. Brew you own coffee instead and put that money to work. Eliminating a daily $3 coffee for example (or donut etc), equates to over $1,000 extra savings per year. The important point here is the thought process; eliminating those unnecessary expenses no matter how small, and saving and/or investing it adds up over time.
Build streams of passive income
Generate passive income such as renting out your spare bedroom on AirBnB, baby- or pet-stting, doing a online blog using Google adsense to post ads and get paid for ads. Divert your extra earnings into savings.