Probably while discussing over a plate of abacha and kanda, the statement would open thus:
'Nne, we've been in relationship for quite some time. I love you and I want to marry you...' Or something like that.
As simple as that. No formal 'kneel-down-with-ring' proposal - it's a charade. What point are you trying to make? No engagement ring - it is useless and irrelevant. No engagement party - it is downright silly and a waste, at least to me.
If her response is positive, we would start making arrangements to visit our families, discussing wedding plans and our future. If it's negative, we will quietly go our different ways.
But I have noticed that some people don't like quiet, private life. They love to publicly dramatize their personal life, assaulting the general public with issues that have no business being in the public. Dragging the rest of us into discussing matters two grown ass adults should handle privately.