The first thing you will probably notice, is that the bitch will become more 'clingy' wanting to be cuddled and following you round.
Physically, a slight thickening round the waistline - not so much 'tuck up' just in front of the hips. Most probably sign is that her nipples will become pinker and harder, and stand out a bit more than usual.
She probably won't want to eat any more just yet, but nearer the end of her pregnancy you should split her feeds so she doesn't feel so bloated.
I would speak to your vet about worming, I always use Panacur liquid, which you give to the bitch every day from day 42 until two days after whelping. This makes sure the puppies are wormed inside the mother, and they should be born with very little worm burden.
Keep her exercised as normal, and in fact, don't do anything different until the last couple of weeks. Give her somewhere where she can have her babies in a darkened quiet area, and let her get used to sleeping there.
Good luck, there's no sensation like seeing a puppy being born. Hope it all goes well.