Setup of Rock64 using the jumper-and-sd-card method to flash an eMMC.

Prepare bootable SD card

Use Etcher to create a bootable SD from a Debian image. (I used a Stretch Lite image )
By the way, be sure to use a good quality, fast read/write speed micro SD card with ample space, such as this SanDisk 32GB card. You will notice better performance.
Insert SD card

Setup serial console

Attach serial console cable on pins 6,8,10 (same as RPi3). You can use a USB to TTL converter cable to connect. Note that some "FTDI" cables have problems with the 3.3V levels that the ROCK64 serial port uses -- the cable I suggested uses the SiLabs CP2012 chipset, which can handle 3.3V.
Use eg picocom or screen to connect to serial console. Settings are: 1500000 8N1
- picocom --b 1500000 --d 8 --parity n --stopbits 1 /dev/cu.SLAB_USBtoUART
- Note that some FTDI cables may have problems with the 3.3V logic the ROCK64 provides

Boot with both eMMC and SD card visible to OS

Attach F-F jumper to two pins next to "Recovery Btn" on board
Power-up to boot. You should immediately see text output in the serial console.
When uboot boot timer is visible, hit any key to stop boot
Remove jumper
Type boot to continue boot process
Login is rock64/rock64

sudo fdisk -l : should see two kinds of devices in the list:

/dev/mmcblk1xx   This is your SD card
/dev/mmcblk0xx   This is your eMMC module

If you don't see the right devices, reattach jumpers, sudo shutdown -h now, power down and retry.

Flash eMMC with initial image

If all looks good, create a file setup.sh with:

curl -L https://github.com/ayufan-rock64/linux-build/releases/download/0.5.15/stretch-minimal-rock64-0.5.15-136-arm64.img.xz | unxz -c > /dev/mmcblk0

sudo chmod 0754 setup.sh
sudo setup.sh this should cause the image to be downloaded and installed to the eMMC
Shutdown, remove SD card, and reboot

Setup Wifi

Insert Realtek 8188eu -compatible wifi usb dongle
Edit /etc/wpa_supplicant/wpa_supplicant.conf :

country=US
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1

network={
        ssid=<SSID>
        psk=<psk>
        scan_ssid=1
}

Look for the generated wifi interface name by doing sudo ifconfig -a -- it's not eth0, lo, or p2p0 , it is something like wlx0013ef801bc3 -- copy this name
sudo vi /etc/network/interfaces and append the following:

auto wlx0013ef801bc3
allow-hotplug wlx0013ef801bc3
iface wlx0013ef801bc3 inet manual
wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf
pre-up iw dev wlx0013ef801bc3 set power_save off
post-down iw dev wlx0013ef801bc3 set power_save on