Since this is a bronze-age city, there is no reliable contraception, so anything which encourages marriage will also encourage population growth.
Assuming you have leet social engineering skills, I'd try
1) Elimination of dowries. Couples can marry young.
2) Discourage marriages within clans. This is actually something of a problem, since bronze-age societies were quite violent, and social groups were quite close-knit - at least, the ones which survived.
3) Riffing on 2), make outmarriages the accepted mechanism for preventing inter-clan conflict. In effect, the widespread intermarrying will tend to break down clan barriers. Don't expect miracles, though, especially in a bronze-age society where long-range communication and transportation (and I mean more than a few blocks) is difficult. Communication is essentially entirely face to face, since literacy is almost non-existent and cheap printing and paper are unknown. Figure on a combination of political and religious pressure. This is decidedly non-PC, since the historical uses of intermarriage seem to have favored shipping off the girls, not the boys (who are needed at home as warriors).
Furthermore, fast population expansion is a problem, since this implies fast resource expansion. With agricultural efficiency low, large populations imply large farming areas surrounding the city. As these areas expand they will tend to start splintering into local political units, with all the problems of political struggle and war which that implies.