We all know how fidgety it is to flash the ESP: 3.3 volts only, smoothing capacitors, GND-GPIO 0, VCC to CH_PD. Wouldn't it be nice if there was a simple adapter?
A quick look in ebay reveals that at least for the ESP-01 you can pick up a cheap little adapter something like this:
I bought one a few weeks ago and plugged it in. Not much happened - and it certainly wouldn't flash the ESP. I looked around for instructions and couldn't find much, so I put it in a drawer and forgot about it.
The other day I came across this. Apparently you need to ground GPIO 0 manually. The link shows an elaborate contraption to do this.
I pulled mine out of the drawer and used 1cm of wire to do this: