They banned newspapers. From 1910 until 1920, Korean newspapers were forbidden. In 1920, the government began it's cultural policy (bunka seiji) which took a more relaxed view on Korean cultural things. The Chosun Ilbo and Donga Ilbo were founded that spring (and are still two of the largest papers in Korea). Organized activities (sports, scouts, religious activities, labor unions, etc) had been banned, but were allowed again in 1920.

All of this coincided with an INCREASE in the police force, the logic being that by allowing people to gather and express their opinions openly, it became easier to watch them, especially with an expanded police force.

All of these freedoms were still very limited. Criticizing the government was still a bad idea and censorship was still prevalent. By 1925, the Japanese passed the "Peace Preservation Law" which gave the police more powers and curtailed some of the previously granted freedoms, so the relaxation was only for a few years.

They required everyone to register at a Shinto shrine. The governor general, Minami Jiro (1936-1942) pushed for a unified Japan/Korea. Everyone had to register at a shrine and all students and government employees were required to attend ceremonies there.

They changed everyone's name. In 1939, the "Name Order" came down requiring people to take Japanese names. By 1940, all government workers, school children, or anyone affiliated with the state had to have a Japanese name. Approximately 84% of Koreans did this.

They suppressed the language. In 1940, all newspapers had to print in Japanese, with the exception of the Korean edition of the official government paper.

All Korean language books stopped being printed and speaking Korean in school was punishable. By 1938, the Korean language was being forced out. By 1940, books were no longer printed. By 1943, using Korean in school could get a student punished.

For more information, see A History of Korea by Michael J Seth, pp296-97, Forced Assimilation.

A number of the mainstream historiography (in the English language at least) takes a reductive approach into colonial Korea, seeing their domestic issues as struggles of being 'pro' or 'anti' Japanese. However, it was not necessarily that clear. For example, Chang Chiyon, a leading editor for the paper Hwangsong sinmun, was, like many Asian observers at the time, impressed with Japanese reforms. He promoted reforms through his editorials to follow similar lines of Japanese achievements. In 1904 he even imagined an East Asian Alliance of Korea, Japan and China against Russia. However, Chang swung the other way once Japan 'broke Korea's trust' by its imposition of protectorate status. His scathing attack in 1905 got him arrested and within two years Japanese restrictions did increase on Korean publications.

Yet the colonisation of Korea was not necessarily a clear, long-term Meiji goal from the start, as contended by scholars such as Duus. In Abacus and the Sword, he states that colonisation decisions took place due to complex agencies, from journalists to businessmen, uniting the Meiji leaders to take action. Duus looks at economic and political forces at play, pushing the 'Korean question' to the top agenda of foreign policy. Duus acknowledges that the Japanese decision makers defined Koreans through derogatory means to help justify their 'guidance'. This could have been projected under various themes. Hygiene was one of the themes to promote Japanese progress and create the 'other' in the colony, as presented by Henry in Sanitising Empire.

In The Japanese Colonial Empire, 1895-1945, Ching-chih Chen's article on the police and community control system outline some of the methods in which Japan organised its administration in Korea. Propaganda naturally played an important role, as the established Korean Colonial Cinema Unit spread policies of 'Japanisation'.

I hope this provides some insight and interesting thoughts.

Sources:

Colonialism and the Korea Problem in the Historiography of Modern Japan: A Review Article by Andre Schmid

Korean Cinema During the Colonial Period by Hyongshin Kim