Okay, so white...
This was for my 'simple/speedy-mode' of painting. I don't have much left to me, my eyes have been going for a couple of years.
It's quick, it's dirty and SIMPLE...
First, prime the Mini. With white, I use GW white primer. It's just a consistency issue. With the newest formula, it is less prone to suffering humidity variance AND doesn't chalk up on its own (well, I haven't had that issue in 4 cans now, so I have to assume it isn't just luck).
If I am painting a small(ish) unit, like Death Company, in order to be certain of complete coverage I utilize a set of forceps. It forces a model by model priming, but leaves me with fewer recoats.
Once I'm primed, I double check the model inside (with even lighting) to find out if I missed ANYTHING, as with all white based models you don't have the luxury of counting on your base color covering up any missed spots.
I then use a 002 micron pen to blackline specific areas on the model that I need emphasis on the shading. This is entirely up to you as to what you consider important to shade, but try to maintain consistent light sourcing for the unit.
I then choose my wash. In the case of the DC, I used Badab Black wash (though the Vallejo wash is exceptional for this as well).
First, I run wash into all the crevices/nooks/plates that I blacklined. This step is pure wash on a brush, drawn in thickly. Partially to dull the shine that you get from the micron pen, and partially to blend that darker region outward into the larger surfaces.
I wash nearly all the remaining cracks/joints etc. Do this with a watered down (heavy wet brush will do, or a 1:3 ratio of water to wash) mix. This will create an effect that is cohesive to the model's overall shading, but less strong than the areas that were first blacklined.
THEN, paint all the metal areas black. Black is going to be your biggest bane, as it will require care to not OVERLY destroy your white surfaces. It will happen, you will do it...but this is why we go to this stage BEFORE blending out the wash from areas that are supposed to be clean white....you will be cleaning up any mistakes when you are blending/covering wash. You will also wash your metallic areas at this stage, as it will emphasize delineation between armour and weapons (etc) with ease, and may correct a few spots of black overbrush by expanding (slightly) your shading there.
NOW you will start painting white on all the surfaces that you do not wish to show the wash. How far back into areas of shade you wish to go is how dirty/shaded you wish a model to look. Try a little deep, closer to the crevices, but with a slightly wetter brush. The white will go on thin, and allow a bit of the shade to show through. Back off a bit from the shaded area and repeat, with a brush that is only wet with paint. One final coat, just a bit further back from the crevice, with a brush only wet with paint should do the trick. For this, I use Vallejo white. It is the easiest, and least inherently glaze-like, that I have worked with. GW Skull White is fine, but begins to change consistency the longer you have the bottle.
After all this, you will begin to finalize details, refine shading and add other colours (such as purity seals, red marks for DC etc etc)...but WAIT UNTIL YOU HAVE BASED THE MODEL.
Shaded white does not look like other models, and if you start your color additions before you have finished your basing, it may come out looking a little weird ( I have redone my purity seals thrice now, and still am unsure).
This is NOT golden-daemon quality, but is an interesting and quick method for applying white to power armour(ish) units with speed and not-too-shabby tabletop quality.
Hope it might help a bit, if not then bugger off 'cause yer a better painter than I am!