I had asthma as a kid, more allergy problems than asthma, and I more or less grew out of them, except some of the allergies. I noticed for me, having a good diet and getting more exercise helped. So it's pretty cliched sounding advice, but uh, diet and exercise do help, I think. I think one of the nails in the coffin for me and asthma was daily cycling and walking for about a year or so, that and eating a majority of my food cooked myself from scratch. For me, though, it wasn't really exercise triggered, so that might be a different dynamic. Supposedly, the last time at an asthma doctor after the cycling, I'd had like 5-10% better lung capacity than average.
I dunno, probably not helpful much...