The main indications for adjustment are

If the student can't get the raising leg to vertical (because of tight hamstrings and/or a flattened curve in the lower back), it's possible that they would strain their back muscles or injure a disc if they reached for their big toe. The student should avoid the normal variation and use a strap and possibly bend the lower leg.    It is important that the back of the trunk, the buttock should remain on the floor. 
 

You may also notice that the student is arching their lower back or using their shoulders to lift the leg.  This will be likely caused by weak muscles, and again the student should avoid the normal variation and use a strap – need to   make sure that the full length of the students back is resting on the floor and that they keep their shoulders and neck relaxed.   The variation shown above should be achievable for most students.

The distance between the rib cage and the hips is closer together on the side of the lifting leg (something I need to work at minimising).    Counteract this tendency on the side of your lifting leg by pressing the side of your pelvis away from your head to lengthen your waist, while dropping your leg from your heel into the hip and bringing your buttock into the floor.

Foot of the leg on the floor may tend to drop down loosely.    – Place one can use the support of a wall. You must place the bottom foot against the wall and the hinges of the ankle on the floor.