In Things Fall Apart, a person achieved upward mobility in the tribe by cultivating a large and prosperous farm, by dispensing practical wisdom or profound sagacity, and/or by acquiring a reputation as a fearless and noble warrior.
The book's main character, Okonkwo, becomes famous as a young person for his skills as a wrestler. Later, he becomes a tribal elder, in large part due to his acquisition of yams, cattle, and other farm goods. Okonkwo's patriarchal governance over his wife and children seem important in terms of upward mobility as well, though the various characters have differing notions of the extent to which he ought to be rewarded for this. Okonkwo himself speaks plainly on the subject, noting that: "No matter how prosperous a man was, if he was unable to rule his women and his children (and especially his women) he was not really a man (pg. 37)."
In Things Fall Apart, upward mobility depends upon pprosperity, wisdom, skill at fighting and hunting, and (at least to some extent)strong patriarchal command of the household.