Do the exercise as slowly as you can in the beginning, and don't add any weight until you can do 30 reps (15 on each leg, in one continuous set). Concentrate on balance and smoothness. You will find that the knee of the working leg will need to move inwards (this is to achieve single-leg balance). Keep this movement controlled and feel how balance is being achieved. Very different to squatting on two legs!
Find the audio file of this video at https://supplementary-material.s3.us-west-2.amazonaws.com/Single+leg+squat+variation.mp3.
Nice exercise for all levels. Perfect timing for me to do while I can’t use arms shoulders until stitches out.