Publishing can involve a wide range of skills and knowledge
Many other abilities can be helpful, depending on the job
While some publishing houses in this sector have well organised internship programmes. However, in many cases speculative applications and knowing the right people can the right time can be important, especially at smaller publishing companies
Important things to remember are
Being aware of news, developments and issues in the industry can help at interviews
Here's some news sources you may want to try, more can be found in Insider Views
UCAS defines commercial awareness as understanding "...the economics of the business. Understands the business benefits and commercial realities from both the organisation's and the customer's perspectives"