Here are some steps I've used to set up AdWords conversion tracking for Contact Form 7. This assumes you are already using the Contact Form 7 plugin.
Install WordPress AdWords tracking code plugin:
Create a new page for thankyou/confirmation in the WordPress dashboard:
Pages> add new
Insert AdWords conversion tracking code to the Google AdWords Tracking Code box that appears in the new page in 'edit' view.
Publish the new thank you page created and note down URL.
Go to Plugin>Contact Form 7>Settings
Select 'edit' under the contact form in use
Scroll down to find the 'Additional settings' box and paste in this code using the new URL for the thank you page just created:
add code: on_sent_ok: "location.replace('http://www.yourdomain/thankyou');"
Save the update