Good, I'm familiar with acrylics.
Using a watered down dark colour is great for areas such as belts, buttons, etc. to make it stand out more. On clothing, not so much if you are relying on gravity to fill in - you tend to end up having shadows where they shouldn't be. On cloth folds, the dark area should be on the underside, but you can't control this if applied like a wash.
You can still apply as thin paint, but it has to be applied with precision - this means one fold at a time. It is more work, but will be worth it in the end. An overall wash should be relied more on tying things together, adding a slight variety in shade,or if you find there is too much contrast.
I would suggest looking up Marion Ball on youtube. Her's is a tutorial on face painting, but the basics can be applied to other parts of the figure as well. Of course, her's is not the only way, many have posted videos on their own individual methods, just have to find the ones that suit your style.
regards,
Jack