These are the standard praenomina,
from most common to least common.
A praenomen is a personal name which distinguishes an individual from other members of the same family. The praenomen is not normally used on its own: normally only close relatives or very close friends call each other by their praenomen.
Note that each of the common praenomina, and some of the rare ones, has a standard abbreviation. Each abbreviation is unique to that praenomen: a praenomen cannot be abbreviated simply by using its first letter. For example, T. always means Titus, never Tiberius; Ti. always means Tiberius, never Titus.
Most of the time praenomina are abbreviated rather than written out in full, so M. Tullius Cicero is normally seen rather than Marcus Tullius Cicero.
Many gentes and families used only a handful of praenomina. The first child of a marriage was almost always given the same praenomen as the father; the second child was given a different praenomen, perhaps the same one as an uncle or grandfather, for example.
Thus the elder son of P. Cornelius Scipio was named P. Cornelius Scipio (Africanus); his younger son was named L. Cornelius Scipio (Asiagenus) after his grandfather.