What reforms did the Manchus (Qing) introduce and how were they successful?
The primary reform of the Manchu were to end the Ming Dynasty. Ming emperors had secluded themselves within the Forbidden City and allowed court Eunuchs to rule in their stead. Corruption and discontent were widespread, but the ruling family remained blissfully ignorant due to a self imposed isolation. When a revolt broke out, the last Ming Emperor and his family committed suicide.
The Manchu formed the Qing ("pure") dynasty. Among the major reforms they instituted, aside from eliminating the influence of court eunuchs, was to promote scholar gentry to key administrative positions within the government. The scholar gentry were quite well educated and had passed a rigorous three day examination in Confucian principles. Two Qing Emperors, Kangxi and his grandson, Qianlong, expanded into Burma, Vietnam and Turkestan, thereby preventing further nomadic invasions. Kangxi believed that a ruler should provide for the welfare of his people, and instituted flood control, as well as a number of irrigation projects. His administration was so successful and his tax collections so efficient that four times during his reign, tax collections were cancelled, as the treasury needed no more funds.
Qing Emperors were regarded as the "son of Heaven," a title later adopted by Japanese Emperors. His daily life was carefully scripted and he was considered so important that the characters which formed his name were not allowed to be written. Few people were allowed into his presence; those who did were required to perform the ritual kowtow before being recognized.
Even so, The Qing were careful to preserve their Manchurian culture. They would not allow the native Chinese to learn their language, from traveling to Manchuria, or to marry a Manchu. Chinese men were required to shave their heads and wear a small queue of hair as an indication of their submission to Manchu rule.
Ultimately the Qing dynasty fell into the same corrupt status as the Ming, allowing Court eunuchs to administer the government while Qing Emperors busied themselves with their concubines or with hunting. The dynasty soon was in trouble also.