Mr Cameron said that if people did not have the skills required for employment then Job Centre staff would send them on training courses.
For example, people with poor English skills will be referred onto specialist English language training courses and if they refuse to attend any recommended courses, they could have their benefits stopped.
Mr Cameron said benefits should be more conditional on people's willingness to look for work: "We are getting rid of the old idea that you can get your welfare without conditions being put on that," he said during a visit to an employment support centre in London.
"So we are saying that if there's something you need to help you get a job, for instance being able to speak English and learn English properly, it should be a requirement that you take that course, do that study in order for you to receive your benefits."
"That's good for you because it's going to help you get a job, it's good for the taxpayer because we won't be wasting money on welfare that's unnecessary, and it's good for the economy because we want more people in work creating a bigger, more productive economy."