• You don't use an asset allocation strategy. Many investors select individual investments over the years, not considering their portfolio's overall makeup. Add up all your investments and calculate what portion is invested in each investment category. Assess your current allocation and determine whether it fits your personal situation.

• You have too many investments that aren't adding diversification to your portfolio. Diversification helps reduce the volatility in your portfolio, since various investments will respond differently to economic events and market factors. Yet it's common for investors to keep adding investments to their portfolio that are similar in nature. This does not add much in the way of diversification, while making the portfolio more difficult to monitor. Keep in mind that diversification does not ensure a profit or protect against loss in a declining market.

• Your portfolio's return is lower than benchmark returns. While everyone likes to think their portfolio is beating the market averages, many investors simply aren't sure. Review the return of each component of your portfolio, comparing it to a relevant benchmark. While you may not want to sell an investment that has underperformed for a year or two, at least monitor closely any investments that significantly underperform their benchmarks. Next, calculate your portfolio's overall rate of return and compare it to a relevant benchmark. Also be sure to compare your actual return to the return you targeted when setting up your investment program.

• You trade too frequently without adequate research. With so many choices and so much information, it's tempting to trade often based simply on other people's recommendations. Yet, besides the tax and trading costs associated with trades, frequent traders often underperform those who trade less frequently. Instead, purchase investments you are willing to hold for the long term.

• You don't consider income taxes when investing. Ordinary income taxes on short-term capital gains and interest can go as high as 35%, while long-term capital gains and dividend income are taxed at rates not exceeding 10% (0% for taxpayers in the 10% or 15% tax bracket). Using strategies that defer income taxes for as long as possible can make a substantial difference in your portfolio's ultimate size. Some strategies to consider include utilizing tax-deferred investment vehicles, minimizing portfolio turnover, selling investments with losses to offset gains, and placing assets generating ordinary income or that you want to trade frequently in your tax-deferred accounts.