Depends - I'm sorta fussy about my directory structure which means I don't use the DH default - I create a top-level directory for each domain and put the home directory for each subdomain under that so that creating additional subdomains is simply a matter of a copy command. Again, frex:
www.example.com points to "/home/username/example.com/www/
dev.example.com points to "home/username/example.com/dev/
...and so forth. That way if I wanted to make another development site it's simply a matter of pointing the new subdomain to another subdirectory via the DH control panel then just copying the code en masse to the new directory.
Copying SQL data is simply a matter of using phpMyAdmin to Export as SQL from the live database and copying the output then going to the development server and paste the copied SQL for execution. Unless you're like me and spent $$ on a good remote SQL client that can do that for ya.