I used to have a set of transfers for the 5th Edition Undead army, but they are long gone and have been out of production for a decade or so. GW has just started to bring back water-slide transfers, but so far has only released sheets for High Elves and 40k.
So I set about making my own. I have been asked to provide a tutorial, but to be honest the process has been rather fraught with trial and tribulation, so this is more of a cautionary tale.
First up, you will want either some digital source material or some sweet design skills. I own a copy of Uniforms & Heraldry of the Empire, so all I did was scan the Nuln pages onto my computer.
Next, you will want some kind of editing software. I used Photoshop. I needed to clearcut and touch-up the images, as well as collate them into one sheet.
Once I had the file ready, it was time to print!