In the past the children were usually named after their parents and their parents brothers and sisters. Also through the religious times a lot of Biblical names were used and followed through the years. This custom is still carried out to some degree and in modern times we tend to use and manufacture new names. Surnames as used today did not appear as a rule until the times of the Crusades.
The following pattern was the more common method of giving names to the children and sometimes aids in tracing our previous generations.
1st son after Fathers Father
2nd son after Mothers Father
3rd son after Father
4th son after Father Oldest Brother
1st daughter after Mothers Mother
2nd daughter after Fathers Mother
3rd daughter after Mother
4th daughter after Mothers Oldest Sister