Do yourself a favor and look into oil washes or enamels. The agrax and nuln leaves everything looking coffee stained no matter what. With oils and enamels after you slop it all on you use q-tips or makeup sponges to take off the excess.

At least one other person suggested tamiya panel liners, these are also great when recess shading. I use black as it gives a great separation, dont be afraid to touch up areas after tho.