Instructions can be found here.
For backup reasons, I’ll put them here as well:
Fire up a terminal.
1. [IMPORTANT] sudo cp /etc/fstab /etc/fstab.old – Create a backup of the fstab file just in case something unwanted happens.
2. sudo blkid – Note the UUID of the partition you want to automount.
3. sudo nano /etc/fstab – Copy the following line to the end of the file, save it and reboot afterwards to check if it worked.
UUID=<uuid> <pathtomount> <file system> uid=<userid>,gid=<groupid>,umask=0022,sync,auto,rw 0 0
Examples for the <> variables:
ntfs-3g (for an NTFS partition)
For further reference: fstab tutorial.