Since mass storage device is not always available, exchange files using MTP becomes mandatory.

• 1st, install jmtpfs package or simular (mtpfs, go-mtpfs). fuse is needed.
• add users that need to mount such device to the fuse group.
• create a new directory that will be used as mount point (for instance ~/mtpdev).
• For each file exchange session:
  • plug your USB device (beware, connection some android phone will fail if in standby mode, unlock your device first).
  • mount device: $ jmtpfs ~/mtpdev
  • do wathever you want on the mounted file system (unfortunately, much slower than any mass storage device).
  • Once all exchanges are completed, unmount file system: $ fuser -u ~/mtpdev
  • The device is ready to unplug.

Read more Mount MTP USB device

$ modprobe usbnet
$ ifconfig usb0 up
$ dhclient usb0

Read more Use an android phone as internet gateway