If you want to cross the border to Myanmar by land from Thailand you will need to get a visa in your passport, an e-visa is not enough. You can get this at the consulate in Bangkok or in Chiang Mai. The process is about as simple as getting the vis anywhere else, and here is a first person account of the process of getting a Myanmar visa in Thailand in 2016…
” I went to the Chiang Mai consulate, I was there 15min before it opens. The guy behind the gate gave me a form to fill in (1 page about you and 1 about your previous and current job). After filling that out on the benches across the street, we were allowed in. We as in, me and the three other people who were there.
Bring two ID-photos (white background) and your passport (they need a copy but can make one there).
You have to glue one of the pictures to the document, give it all to the person behind the glass. They check your form, you pay them and done, you get to go back in 3 days to pick it up.
If you need your visa the same day, it is more expensive and you need a reason why you need it the same day. Either a plane ticket or bus ticket out of Chiang Mai will do. I didn’t have one but was allowed to email them a copy before 2pm that day. I picked my visa up at 4 pm.
So easy, so simple, I can recommend it “
With regard to the actual land crossing, it is still much better to fly in to either Yangon or Mandalay if you can, not only is it much less hassle but it isn’t even that expensive anymore. The border towns are still unstable, you’re likely to get totally ripped off when changing money, officials still aren’t sure of some of the rules, -so they say- and may try and scam you, and transport and infrastructure isn’t quite there yet. Although if you are one for adventure, have a go and let me know how it went! There is some great trekking 3 hours north of Tachilek which is still likely very untrodden by westerners. 🙂