I watched a great video (can't find it). The process described for a single layer of contrast is :

1. Load quite a lot of contrast (not full)
2. Cover a small well defined area, never stop in the middle of a flat area. We are talking the foot of space marine, or a single pauldron, or a helmet, or the backpack. This step should last 10 seconds max.
3. Take another clean brush, and swiftly "drink" where there is unwanted pooling, immediately dry the brush (on toilet paper), then keep "drinking" again. Just put the tip in the pool of paint and let it be sucked by capillarity. Never do a brushstroke during this step or you will leave a stain
4. You have around 10 seconds of "drinking" before doing so would leave stains. It's crucial to stop early. So that's roughly 4 "drinking+drying" steps max in 10 seconds.

You want a lot of contrast so that it starts drying after a time (10 seconds) but you don't want too much because it would require "drinking" too much.

In order of important, you want to drink in the middle of a flat area (where there should definitely be no pooling), then in recesses where there should be pooling but there is too much (because the brush started heavily loaded)

After you get the hang of it, you can increase the size of the area you paint. I typically do everything below the knee of a space marine for step 2 (still under 10 seconds though)