Ground the leg your are not lifting, push the thigh, shin, foot into the mat
There's a tendency to lift the leg from the foot but activate the buttock and begin to lift from the head of the femur itself rotating it up in the hip socket, along with the thigh, the knee the calf and the foot, lift the whole leg.
Stretch through the length of the leg
At the end of the inhalation give the hip a little nudge upwards while pushing the other hip into the mat.
As with the leg, rather than just lifting the arm stretch right through the arm from the shoulder to the hand