Count the total number of electron domains around the central atom
Count each sigma bond as one electron domain
Count each lone pair as one electron domain
Ignore pi bonds when counting electron domains
Determine the steric number = sigma bonds + lone pairs
Match the steric number to hybridisation
Steric number 2 = sp
Steric number 3 = sp2
Steric number 4 = sp3
Steric number 5 = sp3d
Steric number 6 = sp3d2
Steric number 7 = sp3d3
Use the molecular geometry only after finding the steric number if needed
For ions, adjust the valence electron count before determining lone pairs
For multiple central atoms, calculate hybridisation separately for each atom