The hundreds of layers on the Viggen's PSD files can be overwhelming at first but they are generally organized efficiently. For really basic livery use the "_1" PSD but for the most available anything use the "_2" (The posted instructions say edit in _1 then paste into _2 but I discovered an offset so just do everything in _2).
To start with - I generally turn off all layers except "Grey" (at the bottom) which reduces overhead and gives me enough to work with to know what I am painting. I colored all the turned on layers red ahead of time so I can turn them all back on to default if desired.
All the painting will be under the Liveries folder - I just create a new folder myself in there named my new livery, then create a new layer. I turn opacity to 70% on the layer so I can still see under to the outline ("Grey") though you could also turn the AO folder on and stay at 100% opacity. You can also turn on the default liveries to see what patterns were where in the same way.
I generally produce 3 layers in my liveries - Nose, Under Body, Body (in that order, keeps the lower part of the fuselage which is usually monotone safe from bleed from the more complex design).
Once done turn on the decals layer - the default layers here are listed as new_decals and new_decals_R "Left" side are always default. I add a custom folder here and then place any roundels and markings into this folder - which places them above the painted layer on the airframe, but will appropriately display weathering from other layers.
From here, turn on the original layers from the beginning - for weathering, lights, panels and vents, rivets, etc. Now save the PSD and then save the DDS.
It was daunting at first but after about an hour of tinkering I figured out what all the layers are and prefer the huge level of options the full PSD they provided give! My 2 cents - will probably make a video for this and post it.
