Two things: you preach it and you see it as the foundation and wellspring of all Christian practice. That’s the essence of being gospel-centered.
Tim Keller summarizes this very well in his excellent article “The Gospel and the Poor“:
So what does it mean to be committed to the primacy of the gospel? It means first that the gospel must be proclaimed. Many today denigrate the importance of this. Instead, they say, the only true apologetic is a loving community; people cannot be reasoned into the kingdom, they can only be loved. “Preach the gospel. Use words if necessary.” But while Christian community is indeed a crucial and powerful witness to the truth of the gospel, it cannot replace preaching and proclamation.
Nevertheless, the primacy of the gospel also means that it is the basis and mainspring for Christian practice, individually and corporately, inside the church and outside. Gospel ministry is not only proclaiming it to people so that they will embrace and believe it; it is also teaching and shepherding believers with it so that it shapes the entirety of their lives, so that they can “live it out.” And one of the most prominent areas that the gospel effects is our relationship to the poor.