Failing to modify stretching movements is the first common mistake made by many BJJ practitioners.
This is where you try to stretch too far too soon, find it painful, then give up before making any progress.
Instead, it is best to gradually increase your stretching range over a period of several months.
Yanking is another similar mistake. It is where you attempt to grab your foot from a straight legged, seated position. Doing this when you are not flexible enough can cause injury.
Not staying in a stretching pose for long enough is the third most common mistake. Most people hold stretching poses for five to six seconds, but thirty seconds or more is best to get the optimum benefit from the exercise.