Using Bootstrap's Offset Classes
Bootstrap 3 provides offset classes (col-md-offset-*) to push columns to the right, effectively centering them.
Example:
<div class="container">
  <div class="row">
    <div class="col-md-6 col-md-offset-3">
      <!-- Your content here -->
      <p>This div is centered within a 12-column container.</p>
    </div>
  </div>
</div>