How to add a heading at the top of node/add or node/edit? In my node/custom_content/edit and/or node/add/custom_content page I want to place a heading at the top of the page as "Create New My-Content".

Seems simple enough, but I am unable to do so. How can this be achieved?
If you mean to change the title of the page you can do this. This will make all node add form titles "Create new [content type]" instead of "Create [content type]".
It doesn't change the edit form because it doesn't make sense to put "new" in the title there because it is not new content, you are editing existing content.

Create a new custom module that implement this:

/**
 * Implements hook_form_BASE_FORM_ID_alter().
 */
function MODULE_NAME_form_node_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  // For the node add form.
  if (!$form['nid']['#value']) {
    // Add "new" to the page title.
    $node_types = node_type_get_names();
    drupal_set_title(t('Create new @type', array('@type' =&gt; $node_types[$form['#node']-&gt;type])));
  }
}