Use anisotropic building blocks
It can be difficult to place a building block which is almost
isotropic (e.g. an octahedron), because all orientations will be almost
equivalent. So it is a good idea to modelize in an anisotropic way, i.e.
with a building block longer than larger. This is especially useful for
hybrid (metal-organic) samples, where this kind of trick can be used.
Avoid Preferred Orientation
This goes without saying, but even if Fox allows ab initio
structure solution with Preferred Orientation, it is always much
more difficult to find it. So try to avoid texture (do not close-pack powders,
etc...). For a strong preferred orientation, it will easily take 10
times longer, and with a low success rate.
At the very least, try to put as much information as you can, e.g. fix the
preferred orientation vector, or limit the March coefficient to values from
0.1 to 1 if you know the crystallites are needle-like , and to values from from
1 to 10 if they are platey-like).