Here's what I do. Keep in mind that I hacn't tried this in two months so some stuff might have changed.
This is for the LG Nexus 5, codenamed lg-hammerhead. It might work on other devices
but I don't know.
Do note: This might be a fruitless effort because Xorg is currently not booting on hammerhead. I don't know if this issue still exists or if they merged the fixes into master so proceed with careful optimism.
It seems I can only get a reliable boot by flashing every time. That being said, we have to flash and what better way other than following the steps detailed on the wiki. We also need the debug-shell so that adds an extra command. Assuming you already built the image, you can do:
./pmbootstrap.py flasher flash_rootfs --partition userdata
sudo fastboot format system
pmbootstrap initfs hook_add debug-shell
./pmbootstrap.py flasher flash_kernel
So you have to telnet in now. Run whatever command it is that lets you see your IP addresses
(I do ip addr because I run Arch) and telnet into the hammerhead. You can run dmesg and look for a new
interface if you don't know which one is the hammerhead.
Once you've got in, you have to boot it manually. Follow the script from line 37 to 44. Do
note that when I ran the commands I had to change line 38, extract_initramfs_extra @INITRAMFS_EXTRA@, to
extract_initramfs_extra /boot/initramfs-*-extra. I can't remember where I saw this but it worked for me and the
other line did not.
After you run mount_root_partition you can do pmos_continue_boot. This kills telnet, I believe.
This is all I remember and can gather from looking at my notes. I wish you the best of luck in your PostmarketOS journey. May the kernel be with you.