You definitely need an accurate scale. One that measures ounces or grams.
Do not cut cords. No need to tie them either. If the bitch does not take care of them, or you need to cut one, mash and shred it with your thumbnails, oir crush it with hemostats and tear it. Cutting will allow bleeding, and leave a pathway for infection to go in. Crushing seals it off, stops bleeding, and closes the inward pathway. No need to tie them either. Some people add a drop of disinfectant. I never have. Whelping is not intended to be a sterile experience.
Use yarn or ribbon to ID the puppies if they are not marked clearly enough. I use yarn at first, and then ribbon. This way you can see at a glance who is on top of who in the box, or who is nursing first, or stealing all the toys, or who is always over in the corner.
Weigh each puppy at birth after you dry and stimulate the puppy. The bitch should do a pretty good job of it, but if you have a slow puppy, it needs rough toweling to help it get started. Use a pen light and check each puppy for cleft palate. Use a thermometer and ky and check that each puppy has an open anus. Stimulate each puppy's rectum to make sure they have gotten rid of the meconium. Write on a card each puppy's birth weight, time, and any other particulars.
Get a good laundry basket, and when whelping starts, put the heating pad in the bottom of it, and cover it with some towels, and put a towel over the top. Each time another puppy is coming, gather up those that are already here and put them in the basket. This way they are not in the way, and you and mom can concentrate on the one that is coming. Once the next one has arrived, but them all back on mom. Encourage nursing. Nursing causes the release of natural oxytocin and stimulates labor and uterine contractions.
Call your vet if:
The bitch is pushing for more than 45 mins and has not presented a puppy
There is more than 3 hours between puppies and you know there is more in there
Walking can also stimulate labor if it appears to be stopped. Walk her ON LEASH, and take towels with you. Pupppies can appear in an instant, and many bitches will take off to find their own secluded area if they are not on leash. If it's dark make sure you take a flashlight and keep a close eye on her.
When puppies are born, the first thing to do is to clear the head of membranes. If you have to do it yourself, hold the puppy head DOWN, and get all the membranes off with a towel. ROUGHLY towel dry the puppy. You want them to squeak in protest if possible.
If your bitch wants to clean the puppies herself and eat the placentas, let her. Offer her broth during whelping for liquids and energy. Lots of girls like vanilla ice cream too. Plenty of fat, and sugar for quick energy.
I could probaly keep writing all day about what can happen and what to do, but these are a few things you can take care of.