I switched Pixie over cold turkey. I didn't have a single problem... If you switch your dog over suddenly, just watch for any constipation or stomach irritations. Not every dog can handle eating it! I'm also sure to brush her teeth more often and clean her beard since food gets stuck in there so easily.
Nature's Variety has a calculator on their site you can use to help determine how much dry/raw food to feed your dog. Pixie is about 3lbs and gets 2oz of raw meat a day. I used the calculator as a guide, but it isn't perfect for every dog. If we have a really active day, I'll give her an extra half ounce or so... And if she starts to feel chubby (too many people treats! How can you say no to that face?!), I cut back a bit on the raw food and lay off the treats until she's back to normal...
Google BARF diet and you should be able to find tons of websites with information on feeding raw.