The good news is the IRS allows for “Foreign Earned Income Exclusion” of over $100k. Which is good if you are working in low tax countries such as the Middle East. There are also Double tax agreements that allow taxes paid to foreign governments to be deducted from your overall US tax obligations. Using a professional tax service is recommended to navigate the exact rules and filing requirements.
I recently used Taxes for Expats, based out of New York city and was pleased with their fast, professional service. They can definitely guide you through the process and assist with filing previous years returns or an extension if you cannot make this tax year's June 15, 2018 filing deadline. The US government has started cancelling passports of certain individuals delinquent in their filing requirements! So putting off your tax filing requirements is not a good idea.
Note: there are some countries that tax worldwide income, similar to the USA. Each country would have their own filing requirements and guidelines. Best to have a read and see if you are affected when working outside of your home country.