One step before the details of what you believe is the question of why it matters. Simply put, what you believe matters because it's what tells you how to live—and something is always telling everyone. Kevin Vanhoozer explains:
One's life is moving in one direction or another, taking one kind of shape or another. As Pascal remarked: "Our nature consists in movement. Absolute rest is death." To the extent that we are always following some direction or other, our very lives are "indoctrinated." The only question is whether the doctrine that informs one's life is governed by the Christian gospel or by some other story, some other script (The Drama of Doctrine, [Louisville: Westminster John Knox, 2005], 105).
In particular for the Christian, doctrine is not mere guidance, but perpetual conformity. Vanhoozer again:
The purpose of doctrine is to conform us to the truth, and we conform to the truth by bearing true witness to what God has done and is doing in Christ through the Spirit. We bear true witness by speaking, and embodying, the truth in love. To embody the truth of the gospel is to live in such a way that one's word and deeds are testimonies to the love and knowledge of God that were made manifest "in Christ" (397).