Editing tutorials

Basics
...
 * Choosing a level editor
 * The wad format
 * Making a door
 * Making a switch
 * Making a teleporter
 * Aligning textures

Tricks
...
 * Fake 3D platforms

General guidelines

 * How to make a great level

WAD editing

 * Choosing a WAD editor
 * Adding custom textures
 * Adding custom sprites
 * Adding custom music
 * Adding custom sounds