There is no ideal preferred orientation. The value is given that there is no 0 0 0 which will run into trouble. Preferred orientation is mainly related to a certain elongation direction or a dominating plane of your crystals. Therefore needles are described by [uvw] and plates by (hkl). For higher symmetric phases like tetragonal, hexagonal or trigonal often [001] or (001) are the preferred growing or not-growing direction (or cleavage plane etc). For lower symmetric structures the needle axis can have a quite strange indexing, although for many phases it is still the [100] or [010], however, it can be also a [120] or anything more complicated. It is mainly recognizable as reflection of the unusual high intensity. Especially in case you do not know the shape of your crystals in the powder you should use enter the indexing of this hkl. Problematic it can become if [uvw] are important because [uvw] and (hkl) are only in cubic system parallel to each other. Often an image of the structure helps since these reflections are very intense which are from lattice planes which are highly packed or show perpendicular a strong modulation in electron density (clearly empty volumes between high-packed volumes).