In SF4 molecule,the lone pair of electrons occupies the equatorial position in preference to an axial position in the overall trigonal bipyramidal geometry
This arrangement is to avoid the lone pair - bond pair repulsion. If the lone pair occupies the axial position, then there will be three 90 degree lone pair - bond pair repulsion and if it lies in the equatorial position there are only 2 such repulsions which prevents distortion of the molecule.