I always do them in water, because I'm too lazy to buy rooting powder. It does often make for weaker roots, so it's a gamble. Once I have a good root system, pot into small pot with very gritty compost. Water just enough to keep it moist. Watch for new leaves. Once it has had several months in the small pot, and a decent tree of leaves, pot up into a pot not too large, with less grit in compost.
Once it's a decent "plant size", I chop it down so it grows more healthy roots and then when it grows back, it's a bushier plant, too.
The flowering is random. Don't ask me when or why. I think Mama Begonia has bloomed only twice in 30 years.
Forgot: house plants you can do cuttings anytime, depending on the type of plant (Christmas cactus has a very regimented growing/flowering period).