And how effective was it? If this wasn't common, were there any other effective ways of integrating conquered territory?
Pretty common. Italy tried to assimiliate South Tirol and encouraged Italian migration there. Russia tried to russify especially Poland and the Baltics. German tried to germanify polish parts of "their" Poland.
Hungary tried to magiarize Slovenians, Ruthenians and others.
It mostly never worked anywhere 100%. But you nowadays have large Russian populations in the Baltics, large Italian population in South Tirol and former (Austro-)Hungary has populations of them over the whole area.
Just some reading for your entry into that theme http://en.wikipedia.org/wiki/Italianization http://en.wikipedia.org/wiki/Russification http://en.wikipedia.org/wiki/Magyarization