The French and America both fought the British.
The Americans were united against Great Britain, fighting for independence, which made it more of a Civil War. The French Revolution was also a bit of a civil war, with the peasants fighting against the aristocracy and the church. The Americans had a clear vision of setting up a representative type of government, while the French moved more into a state of anarchy and indiscriminate violence. Some of the French who had helped America in her revolution were inspired by the American revolution to pursue revolution in France.
One similarity was that a factor in starting both revolutions were unfair, high taxes.