The number one thing to watch out for is to be very wary of your assumptions. If you previously lived in that country and now you are living in the U.S., your perceptions will have been changed by your experience here. Your data may also be out of date depending on how long you have been away. If you have never lived there, you need to embrace the fact that you really don't know what you don't know. Every assumption can be suspect.
For instance: You may see a piece of statistic that indicates very high smart phone penetration for young adults in a high income bracket in a major city in a developing country. You might decide to bring a mobile first, cloud based SaaS offering to serve some need of theirs. But what could go wrong in a situation like that? First, wireless connectivity could be spotty in certain areas. Second, the reliable availability of electricity is not to be counted on in even highly prosperous areas of major cities in some of these countries. You might find that these mobile devices run out of battery power on a regular basis and there are very few workarounds. These are issues that will simply not occur to people who haven't spent time in the target countries.
Another example is to make assumptions about similarities of countries in a geographic region merely based on their physical proximity or language spoken. For example, many multi national conglomerates classify their Asia Pacific region as APAC - less Japan and Japan, because Japan is so different from the developed markets in the APAC region. While Americans like to lump Latin American countries together as a region, the policy / compliance requirements for each Spanish speaking country is different - learning how to do business in Chile does not necessarily mean you know how to do business in Argentina, or Peru, or Mexico, or Colombia, let alone Brazil.
The general rule of thumb is that you should still make hypotheses to test, but just be extra wary of your own assumptions and biases and know that most of the unspoken assumptions will probably be challenged in some way when you do field work in the country. An open mind is more important here than in research programs run in the same country you reside in. Just spend a lot of time there and live there for a while - you will learn valuable insights that will save you a lot of time and energy later on.