Another vote for the FB group Wolfiefan and MellyPapa mentioned, their Congratulations on Your New Puppy pack is absolutely brilliant.
Start getting them used to being handled all over, including their feet and having their ears, eyes and mouth looked in. Also crack on with nail clipping and teeth brushing early. Particularly with nails it's so much easier (and better for the pup) to make it a positive experience and keep their nails short right from the start than trying to get on top of it once they're an adult.
Don't just go to the vet when you have to. Short, positive trips to the vets (i.e. pop in, give them some treats, maybe let the receptionists have a cuddle, etc.) when they're small will stand them in good stead for necessary trips when they're older. A lot of vets run puppy parties which can be good for this although check how they're run before signing up. A room full of puppies just running riot together whilst the humans chat can end up being very counter productive.
Even if the pup seems fine on their fist car trip home it's still a good idea to build up some positive associations with the car. Feeding them and giving them treats in there then building up starting with very short trips.
Find a decent puppy class (the aforementioned FB group can recommend someone for you if you post, they've also got a list of good trainers by county in the 'Files' section) and pick your insurance (so it's ready to activate in time for when the cover from the breeder runs out) before the puppy comes home.
If you can, sectioning off an area (and preferably a boring one) of garden rather than allowing access to all of it can really help with toilet training as there's less for them to get distracted by. I blocked off a paved area just outside my utility room for puppy training and it's been so useful I've had it properly fenced off since. I don't mind the dogs going in the garden when we're out there but it's so much easier keeping on top of poo picking when most toilet trips are just to one particular, easy to clean area. That said I do have four dogs so more poo to deal with than most!