Credit card acceptance is very low in Myanmar. Carry cash!
When I was in the country, I noticed that only large hotels, airlines, and some travel agencies accepted international credit card payment
None of the local shops, restaurants, and other businesses accepted credit cards. Although I'm sure in Yangon and Mandalay you'll find very high end businesses accepting cards. But for most travelling expenses, for all intents and purpose cards are not readily accepted
So, either bring lots of USD to convert, or use the ATMs to get cash as you go. I saw there are lots of ATMs available in the major cities and tourist regions (Yangon, Mandalay, Bagan) so you don't have to worry about not being able to find one. Just have your bank card read
On a related point, cash USDs are not really accepted for payment much anymore. Up until 3-5 years ago travellers could pay for things directly in USD, but now most businesses prefer cash kyat, the local currency, for payment from tourists
If you're an American citizen, you should call your credit card issuer before you travel to Myanmar. Because of the various sanctions the US government has imposed on Myanmar, some US banks will reject any charges you attempt to put on your card in the country. When I was researching for my trip I came across a lot of American travellers whose cards were rejected when they tried to use it to book flights and pay for hotels. If you're European you should check too just in case. This isn't much of an issue for travellers from elsewhere