Get US dollar
Before you go, if you plan to bring US dollar bills to spend or exchange in Myanmar, you should pay attention to the notes condition. Although Myanmar government has recently told the banks to accept more than just the most pristine of foreign currency, bills that are not perfect may still be rejected or exchanged at a lower rate.
It is wise to consult your local bank a couple of weeks in advance to let them know you need pristine bills that are neither creases nor smudges. Once you get them, treat them well and make sure not to fold them during your journey.
If you happen to be in Asia already, the exchange counters at the airports are the best and least painful options. For instance, Bangkok's main Suvarnabhumi airport is an excellent place to get clean US dollar at a very decent rate.
Exchange US dollar
The best places to exchange are at the airport (during regular hours) and the banks. They offer the best rates and the security that you will get what you should be getting.
Moreover, banks are now found throughout the country, and even smaller towns off the main tourist track like Pindaya have banks you can exchange at.
Anywhere remotely close to a tourist spot (Yangon, Mandalay, Inle Lake, or Bagan) will have standalone places for exchange as well.
Note that most banks are closed on weekends and holidays, as well as being closed for a week every April during Thingyan water festival.
You can also exchange money at your guesthouse or local jewelry shops, though the rate will likely be poorer (MMK 30 / $ less is fair) than what you would get at the bank.
Contrary to what you can read elsewhere, we do not recommend you exchange money on the streets. First, as the economy opens up, selling dollars on the black market has lost its appeal. Moreover, this is a great way to get scammed, particularly in Yangon.
As it is often the case, larger bills (US $50 or US $100) in Myanmar are exchanged at slightly higher rates than smaller bills. Also remember not to exchange everything to Kyat, it can be handy to keep some US dollar in your wallet.
When you leave the country, you can exchange your kyat at the airport or banks before you take off. Keep in mind that nowhere outside of Myanmar will be interested in exchanging your extra Kyat, make sure you get rid of them before you leave.