There is no specified order in which the Vedas can be read. However, since the Rig Veda is the oldest and most important of the 4 Vedas, the Rig Veda can be read first.
For further reading check the following articles:
|Prehistoric Age in India||Prehistoric Rock Paintings|
|NCERT Medieval Indian History Notes UPSC||UPSC Mains Question Papers (2013-2019)|
|NCERT Ancient Indian History Notes UPSC||NCERT Modern Indian History Notes UPSC|