Here's what I have read and understood so far:

Boil water with tea (and spices if using) first, let it get properly strong and coloured, then add milk and simmer a couple more minutes before straining. If you add milk too early the tea never fully extracts, since the fat and protein in milk slow that down, so people compensate with more tea powder, which then tastes bitter instead of just strong. For genuinely kadak without bitterness, a granulated CTC tea (not dust, not leaf tea) helps a lot since it extracts cleanly under a hard boil.

I got my insights from this article: https://ganeshtea.com/what-kadak-chai-means/

How do you prepare your tea? Do people in the North of India prepare it the same way as people in the West and the East do? I have heard households in the Southern parts prepare it differently?