Hi Usurpator, i understand what your asking and here is a quick description of how i do it
Glaze: if i want to glaze the entire surface with a colour to create a richer colour or to tie in my highlights with the base colour heres what i do
1: I get my ink or my paint and thin it down with water, the amount i thin it is purly based on how strong i want the over all colour to be in the end.
2: I then dip an old brush into a pot of washing up liquid, i get just the same amount of washing up liquid on my brush as if it were paint, so you dont need tons, and i then mix this into my watered down paint or ink.
3: Finally (you can miss out this step if you like) i add a drop of Vallejo Matte medium, just to take away any shine that may result from the ink as it dries.
4: i paint the entire area with this mix and the result is as if i had used a very thin trasparent paint over my model
Wash: Ok so if i want to use ink to get into the recesses of the model, say for example i want to define the lines of a face heres what i do
1: get my ink and water it down to the consistancy i want
2: add a small dab of PVA glue ( i read somewhere that it pulls the ink into the crevices if you do this)
3: a small drop of Matte medium (to take away the shine)
4: I Flood the area im working on and allow the ink to run into the recesses of the model, then wait for it to dry
5: i would then use my base coat paint (so for a face a flesh colour) and tidy up all of the high points leaving deep shading in the recesss of the model
One Warning, using PVA Glue in your paint will mess up the brush your using over time so use an old or a cheap brush to apply the paint, also PVA will dry shiny, so you need to take that into consideration before you use it, and make sure you dull coat once the model is dry.
Hope you find this useful:beer: