Well before you get to the washes, you can achieve some good faded, patchy look in the camo pattern during the initial painting phase.
Prime the model in a light color, preshade the panel lines. Start with a thin base coat of the tan color, don't try for even coverage, leave it thin in some places and thicker in others. Then spray on your camo colors using the same technique, leaving it thin in some spots so a hint of the base coat shows through. You can also mix lighter shades of each camo color and apply patches of that to break up the colors.
After that you can try what we armor modelers do and use oil paints and the dot method to create tonal changes in the colors. If you gloss coat with future or any other acrylic gloss first you'll have a little more control, however if you apply the method straight to flat colors it gives it a grainier sun-bleached look. Just make sure you protect the colors with an acrylic clear coat before applying oils due to the strength of the thinner.
Finally, after that is all dried, you can come back with the oils again for the panel line wash (personal preference of course, I happen to like the control with oil washes).
Keep in mind your decals, those markings will fade too so you may want to apply them before the oil weathering. I like to give the model a thin dusting of a tan color to tone down the brightness of the decals and tie them in to the model better.
Hope that makes some sense.