A long time ago I did a simple step by step guide for creating slippy maps with OpenLayers, mostly as a brain dump for myself back then …
I now finally got to doing the same for Leaflet and some of its plugins and created a Leaflet version, too.
The guide user interface is pretty simple (and still needs some improvements), it basically shows a list of steps on the left, and in the larger frame on the right you can see either the map result, the full source, or just the differences to the previous step.