We get questions like this often, and in every case, the answer varies according to your financial situation.
Julie gives good advice (IMHO). I assume everyone sets aside a 3-6 month emergency fund, and works forward from there.
The investment order I recommend:
1) Max out your 401K contribution to get the dual benefit of saving pre-tax dollars, and reducing taxable income.
2) Max out your HSA account (must have a HDHP to have an HSA account).
http://www.madfientist.com/ultimate-retirement-account/3) Max out a T-IRA or ROTH IRA contribution. A tax-advantaged $5,500/year saving bucket above and beyond the 401K/Roth401K.
4) Invest in a taxable account. You can always invest in a taxable account, so don't kick yourself for having one today. Purchase low fee ETF's >> Total Stock Market Fund / Total Bond Market Fund, and/or REIT's if you want a real-estate component to your investment portfolio but don't want to be a landlord (
http://www.mrmoneymustache.com/2011/08/15/become-a-lazy-landlord-with-reits/)
Also... set your investments up to DRIP - Dividend Re-Investment Program. Each stock trading company lets you re-invest dividends into the stock that generates dividends. In most cases, you'll have to manually specify you want dividend reinvestment for each holding in your account.
Keep up the good work, and all the best!