Given that this isn't something I do regularly, it's handy to have the commands to hand so I don't have to scroll through man pages trying to remember how to do it.
Clear the disk
Initialise it
Label it, then edit the labels created
Format it with a filesystem
Make directories and mount as appropriate, and you're done!
Clear the disk
# dd if=/dev/zero of=/dev/ad1 bs=1k count=1
Initialise it
# fdisk -BI ad1
Label it, then edit the labels created
# bsdlabel -B -w ad1s1 auto # bsdlabel -e ad1s1
Format it with a filesystem
# newfs /dev/ad1s1e
Make directories and mount as appropriate, and you're done!