Consider how the markets traded today:
* Treasury prices were up; yields were lower
* Stocks continued their tumble into the trading range of late 2008
* Commodity prices fell; most notably oil
* Consumer discretionary shares underperformed consumer staples stocks
* Financial and housing stocks underperformed the broad market
Broadly speaking, markets can trade in risk-seeking or risk-shunning ways. How traders treat Treasury debt relative to equities; how traders treat riskier sectors of stocks relative to more defensive ones; how traders anticipate economic growth or weakness in their pricing of commodities: all of these reflect themes in markets that tell you a great deal about the mood and sentiment of large market participants.
Catching those themes early in the trading session is quite helpful for short-term traders. Many ideas can be formulated simply by gauging how riskier assets are trading relative to safer ones.