> I usually paint base colours, then do a wash (watered down acrylic paint), then highlight or drybrush areas. But I usually find my washes are splotchy and inconsistent.
I end up using the premade stuff. Vallejo has dark and brown washes in up to 200 ml containers. Messy, so might want to transfer to eyedroppers.
Washes work best on texture. For flatter surfaces, I'm trying out a palette of dark wash, grey wash, black paint, and grey paint. Separate drops, mixed only as necessary. As said, water on the surface, shake off or whatever the excess. I'm lazy, so just used rinse jar water applied with another brush.

Apply darker colors to recesses, grey to flat areas. You can also apply this wet palette after a splotchy wash dries badly. (: