Agree with corners about the yoga. Unfortunately in the world of athletics you get flexible people pushing yoga and people good at long distance running pushing marathons etc.
Such exercises can be harmful to people with different bodytypes without careful consideration given to the individual athlete.
Most athletes nowadays go with a routine like this Dynamic stretching - workout - static stretching/foam roller.
The issue with stretching that I have found is that without nearly daily work on it you quickly regress. So the hardest part of flexibility improvement is adherence.
On the plus side I think that many normal exercises can improve flexibility. Something like a squat hold is a neat way to improve your flexibility if you are inflexible. If you are really inflexible you an start holding onto to a bar..and just holding that in a full squatted positon.