The market has been extremely volatile during the last couple of months. The first big lesson is so obvious but I doubt many people were doing it when the media was so bullish: whenever all major markets show Head and Shoulder pattern, get very defensive( using Inverse ETFs and selling covered calls).
Furthermore, always pay attention to some warnings as shown by various charts such as the following
From the charts above, we can see that the market is heading into some serious trouble mid-late July. Even some early warnings are give back in March and April ( For Example, Bonds start to outperform SP 500 and Large Cap start to outperform Small Cap).
In reflection, the media ( especially CNBC ) was extremely bullish back in April. Yes we did have a stella earnings season for Q1 2011 but that doesn't justify DJIA can break above 13000 and head to 14,000. A couple of analysts on CNBC were expressing their belief that Dow is heading to 14,000 which no proved to be some big joke. Lessons learned again, media's always late and wrong, charts don't lie.
August and September have been weak, especially September. Paying attention to seasonal analysis and sector rotation would be tremendously rewarding.