How does Maoist ideologies differ from that of Lenin and Marxist ideologies?

Mao rejected some of the key tenets of conventional Marxist theory. Marx theorised that the Revolution had to happen in stages... from feudalism, to capitalism, to a bourgeois (democratic) revolution, then a working class revolution leading to a dictatorship of the proletariat, which would eventually create conditions for worldwide revolution and global Utopian communism (I am simplifying this somewhat).

In the first 30 years of the Chinese Communist Parties existence, this was a massive problem for the Party. They were a relatively small, insignificant clique amongst a massive war of many factions, and depending almost entirely on funding from the Soviet Union. The Soviet Union, however, following classical Marxist doctrine, believed that China was still in the feudal stage of history, which was basically true, there had been no industrial revolution, and there weren't many capitalists, or middle class, except in some of the larger cities, just rich and poor peasants.

Classical Marxist theory dictated that the revolution would only happen in urban centres, the revolution was the logical development of the conditions of capitalism and the creation and exploitation of an urban proletariat. Therefore, the revolution had to happen in the cities. Also, in classical Marxist theory, there has to be a bourgeois revolution first, where the working class and bourgeois would make common cause together.

The Chinese Communist Party, due the issues of funding and ideology, couldn't operate separately from the Soviet Union, and were directed by delegates from the Comintern who didn't really have any grasp of the real conditions of China, or any understanding of the country or its culture. This led to CCP members being constantly told to foment uprisings in the cities first (like Changsha, where Mao was active) and also to ally themselves with the Guomingdang Nationalist party, to bring about the bourgeois revolution first. This repeatedly ended in disaster for the Communists, with repeated massacres in the cities, and suppression by the Guomingdang meaning that they were almost wiped out. After witnessing the failure of these tactics, and several bloody repressions himself, Mao was the only experienced member of the CCP to reject these directives from the CCP, and retreated to the countryside to fight guerrilla war instead, coming up with the classic Maoist tactic later used in Vietnam to such good effect, of surrounding the cities from the countryside. Mao's biggest problem, however, was that there existed no real class enemies in the countryside, because there were no middle class, so he had to adapt Marxism to create his own "class enemies" against which the peasantry would fight against. To do this, he essentially turned the poorer peasants, especially the Hakka and landless peasants, against the richer peasants, and exploited existing local grudges and resentment. He set up his own small scale countryside "Soviets" and fought guerilla war against the surrounding population and towns and cities, basing himself in a mountainous and inaccessible region on the borders of Hunan and Jiangxi. After the Shanghai Massacre of 1927 the Guomingdang (who the Soviet Union had been allied with) ruthlessly suppressed the Communists in Shanghai, Changsha and Guangzhou, leading to the virtual elimination of the party. The only surviving power base was Mao's Hunan Soviet, which the Guomingdang then waged war against, leading to Mao's long march during which he formulated his own version of Marxism, focusing on his own shifting definition of class war, and constant class conflict.

Essentially, Mao was the only communist to reject the Soviet Union's version of classical Marxism... this meant he was the only member from the party's foundation to actually survive the virtual destruction of the party, which finally gave him the authority to reject the Soviet Union's directive, and formulated his own version of Marxism which didn't require an industrial or bourgeois revolution.