The key idea to solved such problem is to study the hybridization deeply. These questions fall under GEOMETRY PREDICTION (an application of dipole moment). You must make notes on which hybridization will be polar/non-polar. Further, there are cases of lone pairs, like if a molecule has sp3d2 structure, will the presence of 2 lone pairs change its polarity or not. Yes, you'll have to make each and every hybridization and then it's cases for polarity and planarity. Our teacher taught us a few of them.
P.S. I may upload the pic of the notes if you want.