Following are the main points of electron pair repulsion theory:
There are two types of electron pairs surrounding the central atom.

           Bond pair.

           Lone pair.
These bond pairs are known as active set of electrons.
These electron pairs (bond pairs or lone pairs) repel each other.
Due to repulsion, electron pairs of central atom try to be as far as possible. Hence, they arrange themselves in space in such a manner that the force of repulsion between them is minimized.
The force of repulsion between lone pairs and bond pairs is not the same. The order of repulsion is as follows:
lone pair-lone pair>lone pair-bond pair>bond pair-bond pair.
Pi-electron pairs are not considered as an active set of electrons.

The shape of molecule depends upon total number of electron pairs surrounding the central atom.
For example:
If central atom has two electron pairs, geometry of molecule will be linear with bond angles of 180^o.
If central atom has three electron pairs, geometry of molecule will be trigonal with bond angles of 120^o.
If central atom has four electron pairs, geometry of molecule will be tetrahedral with bond angles of 109.5^o

According to hybrid orbital model the shape of a molecule is determined by the nature of hybridization in central atom.
According to hybrid orbital model:
Sp-hybridization in central atom gives linear molecule with an angle of 180^o.
For example: C₂H₂, CO₂, CS₂, BeCl₂.
Sp²-hybridization in the central atom gives planar trigonal structure with bond angles of 120^o.
Sp3-hybridization with no lone pair or non-bonding orbital on the central atom gives tetrahedral geometry with bond angles of 109.5^o.
Sp³-hybridization with one non-bonding orbital (lone pair) gives pyramidal structure with an angle of 107^o.
Sp³-hybridization with two non-bonding orbital on central atom gives bent or angular structure with bond angle of 104.5^o.
The larger atoms of group VA and VIA such as phosphorus and sulphur do not use Sp³-hybrid orbital in bond making, instead they utilize their p-orbital which are mutually at right angles. Such elements form compounds with bond angles of about 90^o.