To make a yonkoma, first you should write down what it is about. Make a small summary about every panel.
When you've done that, you should make the panels for the sketch
There are a lot of people who draw them themselves, but I hate it and I always print it. I print my templates from Manga Studio. I'm not allowed to publish those exact templates so I found something that looks alike.
http://langesha.deviantart.com/art/4koma-template-108188869 this link is from another deviantart user. Use it wisely.
First you print or draw it on an ordinary piece of paper. just the rough sketches and the text
Then, if you finished that, print or draw another template on a quality piece of paper and fully draw it.
okay, that was the tutorial you can get from any mangaka. Now yonkoma:
The first panel (ki) always has the setting. You introduce something there, whether it's a location or an idea from one of the characters or just a character meeting another one. Always make sure in this panel to let the re