Good observation, the reason it's falling has more to do with Fundamentals and that Investors are still scared because of the previous GM Bailout. If we look back, we can see it has proven to hold those support levels. As for your question, it's different for each stock really (no one stock is the same). Just put your stops under support, and ride it until your momentum oscillators become overbought and tell you to get out. Hope that helps - Cheers!