Start out with the brushing as soon as you get the puppy and start slow.
Hold it in your lap, pet it, love it, and talk to it in a soothing voice all the while you brush it. Start with small incriments (as much as the puppy will tolerate) like 2 minutes. Do that several times a day and as you go build up the time frame.
I always recommend playing with the feet and checking the teeth a lot during grooming and playtime with puppies. This helps get them used to being touched in those spots. The mouth and feet are generally the "no way" areas for a lot of dogs.