One of the best ways to injure yourself during a workout is to repetitively load your joints in extreme ranges of motion.
An example would be doing depth push ups where you lower your body below the level of your hands. This places a big stretch on the connective tissues in your chest and shoulders, creates a lot of post-workout soreness (which is ironically why people seem to like doing it) and will commonly lead to strains in the shoulder joint when repeated enough times.
It also provides no physiological benefit to the muscles being trained beyond that which would have been achieved by performing your push ups to a regular range of motion.
Simple fitness tip then: avoid loading your joints in extreme ranges of motion!