What steps should I take before transitioning from an ED visa to a Non Immigrant O visa in Thailand?

You can do border run and come back in exemption and apply non o retirement visa. It's good move look few days Laos and come back. Take cash because my friend were asked some lubrication maybe 1000baht when he did same day border run without agent. There's no problems if you can show money when you come back. I did border run between non o to non b and I just went desk to desk and back home and pile of cash save that trip. I didn't pay any tee money but they were interested about financial side and money was pouring out everywhere and the customs officers had a smile on their faces🙏🇹🇭

Why the detour? Why not just apply for non-O in Laos?

First off you can't go to Laos and return same day with a visa. That implies you want to enter visa exempt. It will depend upon your history and the immigration officer you stand in front of

Isn't it quicker to apply for non imm straight in Laos? You need to spend at least a couple of days there anyway

You won't return the same day with a tourist visa from Vientiane. It's at least an overnight stay, possibly 2.

Laos is the easiest border to return through so I doubt you'll have any issues.

There are a couple of things though:

1) You cannot go to Laos and return the same day with a tourist visa. Both of the embassies in Laos require multiple days to process a tourist visa application.

2) You need to cancel your ED extension before you leave. Get a letter from your school stating the last day of your studies and then take that letter to immigration about a week before that date and cancel your extension. They will cancel it and give you a stamp that lets you stay in Thailand until the date on the letter.

If you do not cancel your extension, even if it was going to run out, you will not be able to get a new long-term visa until you do so, and you may be charged 500 baht per day for failing to notify immigration of your change in status, even if you left the country.