The first few times I knelt in front of my Master, the strongest thing I felt was the breaking of that taboo. I was admitting by my position to not being his equal, to be being below him. It felt humiliating, but in the best possible way. I was humble before him.
Now all the taboo is gone for me, and a lot of the humiliation. My favorite thing is to kneel or sit at his feet. Every night (unless he gets to bed before me) I spend some time kneeling in wait for him, and I generally spend that time thinking about submission to him, and about being a good slave.
Kneeling: Kink of the Week