Key PointsMany economists believe the economy will weaken over the next year.History suggests that investors should exercise caution when buying stocks.The right investing strategy can help protect your portfolio against volatility.These 10 stocks could mint the next wave of millionaires › Major indexes, including the S&P 500 (SNPINDEX: ^GSPC), closed out the last month on a high note, experiencing their best quarter in years. However, many econ…