It's important to know that an axial or equatorial lone pair (e-) placement can determine the most stable structure. Ideally, you would want a structure with lower "energy" (less e- repulsion)
For example, in
, there are two possible places (orientations) where the lone pair can exist (axial or equatorial)
The axial lone pair lies will the axis of the molecule, where it strongly repels the e- pairs in the three equatorial bonds.
An equatorial lone pair will sit on the molecule’s equator (plane perpendicular to axis) where it strongly repels only the e- pairs in the two axial bonds.
In this case, because the lone pair only repels two e- pairs in the equatorial position (meaning that it has lower energy compared to the axial position) this orientation is more stable and preferred.