The most important things that the Japanese did to Allied prisoners of war include forcing them to work on things that had military applications and failing to give them adequate food, medical treatment, etc.
Perhaps the most famous incident of forced labor was the use of POWs to build the railway in Burma. By forcing the POWs to work in terrible conditions and by failing to adequately care for them, the Japanese caused the death of something in the area of 100,000 prisoners.
I suppose the most famous example of failing to care for the prisoners would be the Bataan Death March in the Philippines. In this episode, thousands of American and Filipino prisoners who surrendered after the fall of the Philippines were led on a forced march in harsh conditions. The men, already weakened by the fighting, died in large numbers (around 10,000) from sickness and from abuse.
The Japanese treated the prisoners-of-war that came into their hand harshly. They were viewed as valueless and as useful only for manual labour. As the war in the Pacific turned against Japan, their sense of desperation only further aggravated such extreme behaviour - contempt eased the policy of brutality and more atrocities were carried out against the POWs, who were regarded as merely human charter.
For example, in Singapore, about 100,000 Allied POWs were forced to live in cramped living conditions and numerous of them were sent to carry out works, such as cleaning and doing repairs. The usual food given to these prisoners was thin rice porridge, which resulted in cases of malnutrition and starvation. Changi Prison, which was designed to hold a maximum of 600 prisoners, was packed in with over 3000 POWs. Many POWs were also sent under the Japanese regime to constuct a 420 kilometre long railway through the mountainous terrain of Thailand and Burma. Around 60,000 British, Australian, Dutch and American POWs were used as forced labour, which eventually led to the deaths of around 13,000 of them.