Time and regular investments are Investors best friends. Dollar cost average is when one invests a set amount and at set times.  Whether the market is up or down, over the long haul, dollar cost average will enable investors to purchase greater shares because of consistent buying, and not 'timing' the market. 

Your 401(k) or 403(b) plans are great vehicles for retirement.  They enable you to regularly put away tax deferred money, and often a percentage of this money is matched by the employer.  Perhaps the two most common mistakes by investors are not contributing to this plan, and diversification.  Too often investors place all their eggs in this one basket.  Our general advice to clients is that at no time should they have more than five percent invested in any one fund, especially company stocks.