(and then there are Daisy meetings ... wow! exhausting. Now, for a retro spindlers posting to round out my day ...)
If you know you are going to ply it, then don't wash it yet. You wash to remove the sheepy smell/dirt/oils from spinning and to set the twist. It'd be okay if you *did* wash it now, but if you wash and then ply, you'll need to figure out how much twist you want to ply it with without the guide of un-set wool to work with (see the starter notes in the spindler's group files, I think there's info on that there -- if not, beep me and I'll explain more).
Once you have your final skein ready (singles, or plied -- whatever you want to end up with), wind it on a niddy-noddy. Now, don't put the niddy in the water unless it's a PVC niddy. You don't need to, in any case -- before you remove the yarn from the niddy, put some figure-eight ties around the skein (I put one on each of the 4 legs of yarn), then remove it from the niddy. Lay it in the washwater. The ties keep it together. It might get a little disorganized, but not much.
I usually do one wash with a little wool wash or dish soap, then one or two washes in plain water to rinse. Don't agitate the skein in the sink -- that would felt it!
I roll my washed skein in a towel and push on it, to remove most of the water. Then I put it on a hanger and hang it over the bathtub so the final drips don't cause any mischief.
If it's angora, you are supposed to whack it on the counter several times. You can do this with other fibers too, it will felt them a little bit, but not into a single mass. It helps ensure the fibers will stick together well in the yarn, as well as helping the twist to spread along the skein as needed to reach a balance.
(based on a post by me on spindlers, 12/11/2001)