I need to cancel my current work permit / visa and then come back on a 30 day stamp, I plan to do this next week. I will then travel back home in the middle of April and get a new tourist visa there, my new job will then convert this into an non-b / extension of stay for me.

What are the steps I need to take in order to cancel my work permit, do I need to cancel the extension of stay at immigration, can I just fly out and back in of the county to get a 30 day stamp?

Thank you in advance for any help you can give me!

Your work permit is cancelled by you or your employer submitting this form to the work permit office. http://wp.doe.go.th/wp/images/form/wp_cancellation.pdf

You could just fly out and back to get a visa exempt entry unless you have a re-entry permit.

The correct way to do it is to submit a termination letter to immigration to have your extension cancelled. You can do it a few days before the termination date on the letter and immigration will postdate the cancellation so you can leave the country by that date.

Thank you ubonjoe, that is the work permit bit sorted out.

If I am flying out of the country do I need to have my extension cancelled, am I likely to be questioned about it at the airport if I don't get it cancelled at immigration?

You likely will not be questioned at the airport but you might be asked why you did not cancel it when you apply for another extension in the future.

Do I need to do it in a specific order?

Can I post date the cancellation of the work permit as well or do I need to wait and cancel it the same day as my visa is officially cancelled?

They are 2 separate things and can be done however you want. You can cancel your work permit prior to having your extension (it is not a visa) canceled if you want to.

Thank you for your help, so when I cancel my work permit, the extension of stay is not cancelled?

Canceling the work permit does not automatically cancel your extension when it is done. It does make your extension invalid.