you simply play the speaker. some people say that there is no such thing as break in. usually the surround needs a little time to move around kind of like a car engine needs the pistons to move around to be broken in.
Nester just start playing the sub at its rated RMS. Thats "breaking it in"; After a few months the spiders and the cone will soften up even more!! Making it sound even better!! =D
Some subs may have alot of spiders, making it a stiffer sub.
I SLAMMED my subs when I hooked them up, and the sound better 2day =D
But I would start them off with the rated power first. lol