1. You won't get rich.
You knew that anyway. But be prepared for the reality that teachers don't make a lot of money overseas. Depending on the job location, you may get housing included. Most likely you will have to find housing yourself. You definitely will not have a lot of money for luxuries. Just the bare necessities. If you are not frugal or don't want to learn how to be frugal, you need to confront that issue before you sign up. Otherwise you will be miserable.
2. Be open minded.
Bulgaria is not the United States. and that, frankly, is part of its charm. You won't find the foods which you are accustomed to. They do things differently over there. That's the point. Try new things. Experiment. It's an adventure.
3. Third world countries do not have first world amenities.
The electricity may not be reliable. Cellphone service is usually fairly good because that infrastructure is new. Internet cafes abound but wifi is not general available. Secondary and tertiary roads can be well-maintained or full of pot holes and ruts.
4. Curricula will be different from those taught in the U.S.
If you are teaching in a state school, you will run into the gamut of required subjects and methods. Private schools will usually stick to the IB curriculum. If they have an expat clientele, they might even offer a British or American curriculum. It depends on the country.
5. Remember: you are a guest.
The reasons why you go abroad to teach are the same now as they were yesterday. You want to experience different cultures. You enjoy teaching and unleashing the creativity and imagination in young minds. Go for it.