At the time of the French Revolution, the French government suffered from crushing debt, primarily due to the wars and lavish expenditures of Louis XIV. The situation was aggravated by the fact that only the lower classes, the so-called "third estate," paid taxes. The clergy (first estate) and nobility (second estate) paid no taxes. Rather than tax the nobility, Louis resorted to borrowing money, to the extent that by the time of the revolution, over half the total income of the French government went to pay interest on the debt. In a further move of desperation, Louis resorted to selling hereditary titles of nobility, which absolved the purchaser and his heirs from paying taxes forever; but at the same time narrowed the taxable base even further. Additionally, the peasantry suffered from high prices for food, notably bread.
When Louis XVI became King, the situation was no longer stable, and Louis was forced to call the Estates General into session. While in session, the third estate demanded reforms in response to which Louis dissolved the Estates General. In turn, the third estate fled the meeting and reassembled at a tennis court where they took an oath to remain in session until France was granted a constitution. The end result was the "Declaration of the Rights of Man," the first significant development in the Revolution.
Well there were many causes of the Revolution. At the time, the lower classes were not happy with the ruling class (King Louis XVI), as they were being taxed heavily.
During the time before the revolution, there was more political freedom than there had been previously. With this new found freedom, and the rise of the popularity of philosophers and enlightenment thinkers such as Voltaire.
The lower classes were also being faced with famine.