The way I do it is to start with cork slightly thicker than you'll need. I use contact cement available at any hardware or home improvement store. Don't forget to cut a "ramp" on the end that you place first for your strip to overlap, and make sure you apply contact cement to that small surface. Trim off the excess with a cutting implement of your choice, but something extremely sharp, like a razor blade or X-acto. Then, I use narrow strips of sand paper to shave them down to size, testing as I go. I think pros may use a lathe to do that, but you've got to work with what you've got. I buy cork sheet from Music Medic in small squares, but you might find luck with those cork strips they sell for that purpose on ebay and such, never tried them.
