Get a bigger bit of wood?
Robin Wod has posted a lot on this, so he is The Man to answer this one but...
Work with the grain running across the bowl not up and down...as if the bowl was standing on the bark not the cut that felled the tree ...as it were...
use half the log and avoid incorporating the very centre rings of the growth as these are most likely to crack in drying
Store the bowl in a poly bag if you take a break - saves it drying out too fast and cracking
you can cheat and drill out a lot of wood from the centre of the bowl before you start the knife work
All this info from one who has yet to make a decent bowl!
I do have a nice piece of Alder waiting to be worked on though - this time I might get it right!
Carve the walls fairly thin - but not too thin... thin wood cracks less often while drying
