As a US citizen you pay US Federal taxes on your worldwide income, regardless of where you live. However, there are certain credits, deductions and exemptions that you can take, look them up:
Foreign Earned Income Exemption allows exempting certain portions of your earned income while you're abroad, if you qualify. Read the instructions to the form 2555 carefully to learn more.
Foreign Tax Credit allows you using foreign taxes paid on your income as a credit towards your US tax liability under certain conditions. Read the instructions to form 1116 carefully to learn more.
Tax Treaties, if exist between the US and the country where you'll be, may exempt some or all of your income in that country if you qualify. Check with a US-licensed tax adviser in that country.
Itemized Deductions - if you didn't take the Foreign Tax Credit, you can deduct your foreign income taxes on your Schedule A. In most cases, FTC would provide a better benefit, but in some cases you'd be better off deducting rather than taking the credit. Do the math.
Obviously you'll have to check the local laws in the foreign country about their income tax rules and whether you have to pay anything there. Most likely you do (unless tax treaty exempts you, if you're a student working on campus).
