I like to roll my pasta out to a number 6-7 on my pasta machine. Typically, pasta machines go from 0/1 to 9/10. Use semolina flour to prevent the dough from sticking together. I prefer semolina instead of all purpose flour for dusting. I find it is less "cakey" and the ravioli remain less heavy overall. I like the pasta to have a bite to it and remain 'al dente'. Rolling the dough too thin results in the filling breaking the tender layer of the dough. After you make ravioli for the first time you can adjust it to the exact thickness you prefer. Some like it thinner and others thicker- it is up to you!