it is very difficult to retrieve broken instrument from canal.
u need to have endodontic microscopes for this purpose.
but u should check the force u are applying in canal when u are working.
if u are using basic rules of checking instruments and keeping instruments for short time in canal then only one reason is remainig: double check ur technique.
may be the force is more which is creating stress in instruments and ultimately instrument breakage.
i hope this will help u.