One important thing is to never forget "both sides" of the joints, etc. In the long run it is not enough to simply stretch the inner thigh, for example and totally neglect the other, outer side of the hip joint. Actually, while I think of it…the hip is a rather complex joint and needs a proper all around approach.
And the hip is connected to the knees and then you should pay attention to the lower back and the abdominal area as well, since no joint does exist in isolation.
I think this is why I am where I am. As a weekend warrior I don't stretch and warm up enough. And as a goalie in hockey I always concentrated on the inner thigh stretch for spreading out in the splits and never stretched my outer hip for 20+ years. Now having to catch up as this becomes my main problem.