I don’t know how you feel about it, but I’ve never really come to terms with the notion of having to make myself pure, although this is one of Patanjali’s precepts, called saucha in Sanskrit.
I was raised in Catholicism to believe that human beings were sinful, a state which is certainly impure. I would go to confession to tell the priest my impure thoughts and deeds, which had to be decidedly innocent as I was still a kid. It’s taken me years to get over the Church’s notion of mortal and venial sins.
Now, I think in terms of using Patanjali’s Niyama more like affirmations or reminders for creating a healthy relationship with myself.
To help cultivate cleanliness or purity, here is a checklist of techniques that comes by way of Emotional Yoga: How the Body Can Heal the Mind by Bija Bennett.

1. Diet – Consider consulting your body’s needs – eating foods that not only taste good but feel good in your body.
2. Satisfy your senses with the highest quality of influences in what you see, hear, touch, taste and smell.
3. Notice your environment and observe what images and sounds feel like in your body; avoid those that are agitating or abrasive.
4. Make your surroundings orderly, visually beautiful, refreshing, clean.
5. Take time each day to regenerate yourself in silence.
6. Keep external noise at a minimum so you can listen and feel your inner self.
7. Eliminate a habit that trips you up and replace it with something new that frees you – that makes you excited, energised and joyous.

Sattva-suddhi-saumanasya-ekagry-indriyajaya-atma-darsana- yogy-atvani ca

Then, purity, clarity, and well-being of the spirit come to flower, as well as concentration, mastery of the eleven sense organs, and perception of the inner being.*
*The Essence of Yoga, Reflections on the Yoga Sutras of Patanjali, by Bernard Bouanchaud.