you pre-configure the boot.conf and other settings on the same system you use to write the raspbian image onto the microSD card, before you put it in the pi. if you get the config right you should be able to boot a pi headless and ssh to it over your 802.11n/ac/ax network immediately after the first time it powers up.
This question is so apt that it gave me a chuckle. I've done it before, but I had to think about that one for a second. You have to edit the file while the SD card is plugged into a separate computer.
