Heading to Burma next week... I know it's the shoulder of the high season. Is it essential to book tickets ahead of time? If possible, we'd prefer to play it by ear and book as we go. But, since we only have two weeks, we don't want to be too laid back lest we miss the chance to see our destination.
I just returned from Myanmar two weeks ago. We took six internal flights and all were full or nearly full. And know that not all airlines in Burma are created equally. Our local guide only recommended one: Yangon Airlines, where their motto is, "You're safe with us." He wasn't worried about the other airlines' safety record, but their on time record and the number of canceled flights. So I would recommend that you book your flights in advance, on Yangon Airlines.
It depends how many days you spend. If your time are limited, advanced booking is recommended for convenient travel. you can prebook buses too.
We recommend NOT booking ahead for your Myanmar accommodations. We were there in high season and did not pre-book a single room, even Inle Lake, and NEVER had a single issue. Have an awesome time!
With regards to flights don't book, and worst case you can score an overnight bus anywhere in the country.
Mentioned in this answer:
No need to book flights ahead. The flights are like buses there, the tickets are sold to local tourist agencies, hotel tour directors, etc. and you buy from them. Your "guide" will usually handle everything and get the tickets to you the next day, but give it two days just in case.