Freeze dry is how most taxidermists do it I believe if you want to retain the velvet. Keep them in the freezer until you get them to a taxidermist. If you just hang them, the velvet will peel and discolor and it looks like crap very shortly.
If the velvet is beginning to come off, like with caribou at times during the beginning of the hunting season, I've just peeled it off and thrown the antlers in a river/lake for a while, it seems to get rid of the blood. They come out white, so you have to stain it to make it look like normal hard antler, it's not too difficult. Some use a glossy varnish stain, which I don't like, but that's personal preference. I don't really like mounted velvet antlers either, but again, personal preference.