You should try to follow the grain as much as possible. To avoid the crack running of the center, which will probably be the case with brittle woods, make a straight crack from the thick end, then put wedges in the crack from both sides and go very slow. Split the piece through the center and split the next piece through the center of that again. Split it into as many staves as possible. Remember that the piece facing out will become the back therefore you must be carful not splitting it more than the width of the bow.
Some people also use bandsaw cutting their staves.
Working the stave to size When you work the stave you will eventually first have to remove the bark or any excess sapwood. Some prefer to remove all the sapwood, while other choose to keep some of it on the back. It is crucial not to cut through any rings on the back at all, since it is very likely to occur cracks and following breakage during bending the bow. Every little knot or irregularity in the wood must be preserved to prevent this. Do not worry about that your stave looks quite ugly because of these irregularities, twists and bends in the wood will be taken care of later.