If you're using acrylic washes, one tip is to use "wet water" (water with an additive to break the surface tension). The surface tension is what causes washes to pool when you want them to flow. I like to use ox gall, but windex and alcohol also work. Have some wet water in a paint dispenser nearby. When you want the wash to get into the deep parts, first hit the area with straight wet water, then add the wash- you will find that instead of tinting, it gets sucked down. Of course, you can use that pooling to your advantage when you want shading over a larger area- it's a fine balance, so experiment a lot, and simple green is your friend for when you inevitably want to do a re-do! If you want to see that in action try searching youtube for vallejo wash tutorial or something like that.
Alternatively, try water colors for your washes, as when they pool all you have to do is wipe it with a wet brush! That's how I made these (WIP):
