slightly overexposing it and a couple of colour adjustments maybe you will want to start of with some actions to get you going if you do not have NIk Color effex or maybe onone photo effects. Plenty of plugins out there that will do this with a few clicks but they come at a price where as actions you can get for free http://www.thephotoargus.com/freebie...r-photography/
Also, not sure of your 'level' of expertise, but a large portion of portrait shoots is the lighting used in the shoot itself...
(ie: 'soft lighting' vs 'hard lighting')
I have seen this in a lot of action collections. There are a lot of places out there for actions. I use Pure Photoshop actions and Florabella. They have a lot of these type actions to give that milky soft look. Try The CoffeeShop Blog. They have free actions.