$sudo touch /etc/udev/rules.d/99-usb-serial.rules
# 99-usb-serial.rules content :
SUBSYSTEM==TTY, ATTRS{idVendor}=="xxxx", ATTRS{idProduct}=="yyyy", ATTRS{serial}=="ssss"
SYMLINK+="TheNameIwant",MODE="0777"

$sudo udev restart

Will create /dev/TheNameIwant when pluging in the usb-to-serial adaptor.

# add "userName" to the "dialout" group
$sudo adduser userName dialout
# or
$sudo usermod -a -G dialout $USER