(1) By doing evangelism. I know numerous groups that claim to be engaging in "holistic" ministry because they are helping the poor in Chicago or because they are digging wells in the Sahel, even though few if any of the workers have taken the time to explain to anyone who Jesus is and what he has done to reconcile us to God. Their ministry isn't holistic; it's halfistic, or quarteristic.
(2) By being careful not to malign believers of an earlier generation. The popular buzz is that evangelicals before this generation focused all their energies on proclamation and little or nothing on deeds of mercy. Doubtless one can find sad examples of such reductionism, but the sweeping condescension toward our evangelical forbears is neither true nor kind. To take but one example: The mission SIM has emphasized evangelism, church planting, and building indigenous churches for a century—yet without talking volubly of holistic ministry it built, and still operates, many of the best hospitals in sub-Saharan Africa.
(3) By learning, with careful study of Scripture, just what the gospel is, becoming passionately excited about this gospel, and then distinguishing between the gospel and its entailments. The gospel is the good news of what God has done, especially in Christ Jesus, especially in his cross and resurrection; it is not what we do. Because it is news, it is to be proclaimed. But because it is powerful, it not only reconciles us to God, but transforms us, and that necessarily shapes our behavior, priorities, values, relationships with people, and much more. These are not optional extras for the extremely sanctified, but entailments of the gospel. To preach moral duty without the underlying power of the gospel is moralism that is both pathetic and powerless; to preach a watered-down gospel as that which tips us into the kingdom, to be followed by discipleship and deeds of mercy, is an anemic shadow of the robust gospel of the Bible; to preach the gospel and social justice as equivalent demands is to misunderstand how the Bible hangs together.
(4) By truly loving people in Jesus' name—our neighbors as ourselves, doing good to all people, especially those of the household of faith. That necessarily includes the alleviation of suffering, both temporal and eternal. Christians interested in alleviating only eternal suffering implicitly deny the place of love here and now; Christians who by their failure to proclaim the Christ of the gospel of the kingdom while they treat AIDS victims in their suffering here and now show themselves not really to believe all that the Bible says about fleeing the wrath to come. In the end, it is a practical atheism and a failure in love.