About one in a hundred osage trees is perfect, six foot straight section, no limbs or "cat faces" (marks in the bark where limbs have died off and grown over), straight grain (no barber pole as seen in the bark), and off good size. Also with ideal growth rings, that is large dark rings with small lighter (spring) rings ratio, which you can't see till you cut down the tree. Don't pass up sections four feet long with good characteristics that can be spliced as billets into full length bow blanks.
You need to split into staves and seal the ends as soon as possible (I use spray shellac) and store away from insects or spray the bark with insecticide.
Then you need to wait a few years for them to dry.
A friend who has harvested osage and made bows is a big help. Its lots of work and a buddy is a good idea.