Tsar Nicholas II had an extremely turbulent reign, in part due to his own inability to rule. Reasons for his poor ruling: His grandfather was assassinated when he was young, making him paranoid to the extreme; his father died when he was still fairly young, meaning that he was inexperienced at the point of coronation; his wife was German, and so he was very unpopular during WW1; his son was a haemophiliac, and to take care of him, he hired the mystic monk Rasputin, a bizarre man who was hated, and suspected of controlling the royal family/having an affair with the Tsarina/having orgies with Russian Noblewomen; he resisted the industrial revolution with all his might, wanting to continue autocratic reign with control over the Church as well. He went to the front lines in Eastern Europe because the war wan't going well, meaning that he took it upon himself to turn it around: unfortunately, he was not a good military leader (nor was he bad, but the Russian army was in poor shape in comparison to the German), so the people blamed him personally for defeats, rather than subordinate generals. There seem to be many ways that he could have prevented his downfall, but his personality blocked these. These ways included: Sack Rasputin; end the war with Germany; end the "loan" that the peasants still owed their lords after being emancipated late in the previous century; be more amenable to democracy (he shut down three assemblies after they disagreed with him); allowe economic change to take place; end the police state (roughly half the nation was under surveillance from the Okhrana)

I would just like to add onto the other pretty accurate answer. The whole issue at the heart of Nicholas' reign was that of Autocracy vs. Democracy. In virtually every other European nation, and certainly in all the other great powers of Europe, some sort of Democracy grew and evolved over the 19th century. In the 18th century, many of the Monarchies of Europe had somewhat resembled the Tsarist monarchy. But events had changed the way countries were governed, and the way people wanted to be governed. But through all this innovation and change, Russia lagged behind.

Tsar Nicholas II ruled by fiat. He was the font of power in Russia, and all governmental authority flowed from him. He had the power to make laws and repeal them at his will. He controlled the money, the police, and the army through a bureaucratic machine which executed those laws. This was Russian absolutism, and its how his father had governed, and his father's father, and eventually how Tsarevich Alexei would have governed (or so Nicholas had hoped).

All this came crashing down in 1904, when Russia and Japan went to war. Fought over things that didnt matter, the Russian army did exceptionally poorly and lost several major battles and huge chunks of territory. In St. Petersburg, all this was received poorly. The people felt that Nicholas had led Russia into an unpopular war which they were now losing after goals which served the monarchy, not the Russian people. And so they revolted, threw a revolution, and established a parliament (the Duma). Ideally, this was to turn Russia into a constitutional monarchy like Germany. And like Germany, this constitution was designed to repress the lower classes. One key way was through vote shenanigans. For example one vote from a land owner carried the same weight as 45 votes from an industrial worker.

Despite the major restrictions placed on the Duma, it still sought to do its job: Make laws. However, this all contradicted Nicholas' goal of being an absolute monarch. After all, how can you be an autocrat if you have to listen to a parliament? So Nicholas used several legal loopholes and shenanigans to systematically undermine the Duma and strip it of what limited powers it had. He justified this by saying that a constitution granted at gunpoint (backed by the force of revolution) had no legitimacy at all. So following this reasoning, spent the next 10 years destroying the Duma's legislative power.

Flash forward to 1914, World War One. Again, Nicholas led Russia into a war it was poorly equipped to fight. During 1914 and 1915, the Russian armies did extremely poorly, and lost significant territory. On the homefront, average Russians turned against the war, and the Russian government. They blamed Nicholas' Austrian wife for being a spy, as well as Rasputin who was close to Alexandra and besides that had forced the resignation of several popular ministers. And did mention he was crazy? Dude was fuckin nuts.

This set the stage for the February Revolution. Nicholas refused to abandon his absolute monarchy. He tried as hard as he could to prevent democratization and change, against the will of his people. And in these efforts, Nicholas was very successful. He succeeded in blocking reforms until 1905, and then after 1905 he succeeded in reversing what limited reforms he granted. However, all this came back to haunt Nicholas. His inflexibility and stubbornness exacerbated public feeling and only served to deepen public sentiments against him.