Individual form controls receive styling, but without any required base class on the <form> or large changes in markup. All textual elements with .form-control receive  width: 100%.  Wrap label and control in .form-group to add spacing.
  
<form role="form">
    <fieldset>
      <legend>Legend</legend>
      <div class="form-group">
        <label for="exampleControl1">Label name</label>
        <input type="text" placeholder="Type something…" class="form-control" id="exampleControl1">
        <p class="help-block">Example block-level help text here.</p>
      </div><!-- /form-group -->
      <label class="checkbox">
        <input type="checkbox"> Check me out
      </label>
      <button type="submit" class="btn btn-default">Submit</button>
    </fieldset>
  </form>