How to practice ensemble playing and accompanying?

[mishamalchik]

So I'm really interested in a career in music and I realize that concert pianist is not a realistic goal. My mentor told me about a huge demand for vocal coaches, accompanists and ensemble/collaborative pianists. The piano, in my studies, has been a very much solo instrument and I don't have anyone to play with at the moment but I want to build the skills over the summer. How do you practice ensemble playing? What are some of the general skills an ensemble pianist needs to have?