Are you already writing pretty good RT already? If not, I really recommend you do as Tami says and get those tapes, but also attend an Anita Paul workshop ASAP! After attending one of Anita's intense workshops, and lots of practice with the NCRA CRR tapes, I was able to pass the CRR on my first try. I was one of only twenty reporters who passed that particular exam.
How I love saying that! Yes, I realize I had almost 30 years of experience as well, but that doesn't count.
Jane, the suggestion from Tami about the CRR tapes is a very good one.
You can never be too prepared for this test, though it is at a slower rate than the other tests, your realtime has to be very accurate to pass it, that's why it's the easiest test you'll ever fail :)
The NCRA tapes are the place to start. What worked for me was practicing every day with various tapes at speeds higher than the CRR - 200 and 225 wpm. At the end of each week I practiced with the CRR tapes, concentrating on clean notes. The CRR material seemed easier after practicing at the higher speeds. Practice for accuracy, not for speed. Doing tapes at 250 wpm was not helpful. Choose speeds you can write with decent accuracy. Also, realtime (for yourself or attorneys) every chance you get when you work and be aware of your conflicts and untranslates. Add common misstrokes to your dictionary.
Be thoroughly familiar with the NCRA guidelines of what is a misstroke and what is allowed. Write with those guidelines in mind as you practice. The test I took did not have a lot of numbers, fortunately.