Avoid attempting recovery yourself on severely traumatized drives (i.e., turning your computer off and on, using over-the-counter diagnostic tools), as doing so may cause further damage or permanent data loss. In many cases, attempts to repair the drive, or recover the data yourself can cause further damage!

The most important thing to remember is to not make the damage worse. Many drives have been rendered unusable by "trying" to get the data back in unorthodox ways. Freezing, tapping, shaking, standing them on their side are all myths of the trade that can take your data and turn it into mush.