What's the best way to add a form in a node template? I already have a node created with some custom fields, I would like to show a specific form in the detail page of the node that i created (using the node.tpl.php file)

Why? because I need to use some values of the node to custom parts of that form

What's the cleanest way to do this?
The best way to do it is to create a variable for your template in hook_preprocess_node():

function hook_preprocess_node(&amp;$vars)
{
  $form = drupal_get_form('form_name');
  $vars['my_form'] = render($form);
}


Now you can drop the form anywhere in your template as the variable $my_form