There's some who suggest that you shouldn't go because of the oppressive government, that tourist dollars help prop up their regime. I think this is basically nonsense. It's not a huge amount of money, and not much of that will get to the government; if you're a conscientious tourist you can try to use local currency and spend it at small local operations rather than the big tourist hotels and guided tours that kick back a lot to the government. I also think there's a ton of benefit to the local people and world awareness just to have contact with westerners (I would say the same about Cuba, etc. etc.) - isolating the people of the country is a terrible way to affect change ; I think we see that throughout history the best way to democratize countries is through maximum contact with western society.
If you actually want to do something about the Myanmar government, you should boycott Chevron, who pumps a ton of money directly to the regime for the natural gas leases in the north. We theoretically have economic sanctions against Myanmar, but of course the oil companies are exempt from that, just as they were when we had economic sanctions against Iraq. The result is that the people are impoverished but the government still gets plenty of money for its military, since the oil money goes directly to the government, while any smaller businesses that would help the people are not allowed to trade.
I heard the CEO of Chevron on NPR once responding to questions about the Myanmar lease. His justification was basically "if we don't do it, someone else will" (and the stuff in the above link about local schools, health care, blah blah blah). He's definitely right that someone else will. There's no oil/gas in the world that some oil company won't touch. Even if our government had balls and enforced real sanctions so that Chevron and Exxon were forbidden from taking the lease, surely China would step in. CNPC is already building a pipeline through Myanmar and is the biggest supporter of the regime already; if Chevron stepped out, CNPC would step in, and without the benevolent local spending.
Despite that reality, it's a preposterous moral argument that it's okay for us to be bad because someone else would be worse. In that situation you should clearly refrain from the bad action and also try to get the world to stop the worse action. We clearly need more international pressure on China to stop dealing with oppressive regimes around the world, but we also need to start doing so ourselves.
I am the worst kind of liberal (*). I can get all outraged about some indignity and rant about how people should behave, but when it comes down to what I personally want to do, I can always rationalize why it's okay for me to do it.
(* = the most common kind / the only kind )