1. The Mailchimp backend. Go to:

Lists -> Forms [from the desired list] -> For your Website -> Signup Form embed code Choose “Classic form” and chose your options and get the embed code.

2. Avoid jQuery conflicts and problems

Replace the dollar signs ($) in the jQuery-Javascript code with (jQuery), especially the function “mce_success_cb” is responsible for a lot of problems otherwise. Take the Javascript code inside the HTML-script tag and embed it via the action hook “wp-footer” to make your site loading faster.

3. Make your own, custom CSS

Remove the stylesheet link at the beginning of the mailchimp form or modify the style. You could use this reference. You also may want to delete the “err_style” in the jQuery script. Change the labels in the form to the desired language.   Thats it ..  don’t know why they do not offer a customizable no conflict form…