There are websites, books, videos, info from your vet out there.
Biggest piece of guidance:
Never allow the puppy to do what you don’t want the adult to do. If you don’t want them to beg at table, drool or be annoying when people have food in their lap, never ever feed them from there. Dog food in the bowl, dog treats from the hand at least a little distance away from where people eat, etc. People are amazed at our boxers, enthusiastic food lovers that they are, who go under our dining room table to snore quietly with their heads on approved people’s feet as we have a tableful of people eating dinner. They have no expectations of being handed something from the table. Don’t want a dog on a certain chair or sofa, never sit there with the puppy in your lap, and be consistent about rules. Boxers are allowed on leather sofas, but not on fabric.
Accustom the pup to you gently handling paws, ears, tail, mouth, teeth, with lots of praise and love, because they have to develop trust in you to get burrs out of paws, grass out of their butts (yes, you do), doing all-over tick checks, brushing teeth, cleaning ears, clipping nails, checking injuries, giving oral medication, etc. They will not like it instinctively at first, but as their pack leader, they must let you and give in to the bond that will develop. They will learn it’s no big thing and put up with you doing what you need to. Do this during relaxed petting sessions as your four month old gets to know you; watch the body language.
In puppy days, we drop by the vet’s office with the puppy to just say hi, no appointment procedures booked, maybe score a treat, with lots of praise and visiting with front desk staff, socializing as appropriate with other animals, exploring the waiting room, with no one anxious or worried. None of our dogs have ever been afraid or worried about going to the vet, even the visits where they get shots or bordetella mist up their noses or invasive exams or the Final Visit.
Have a “dog medicine cabinet.” Medicated spray for itchy spots or small cuts. Ear cleaning solution. A box of Success rice (the packets of parcooked rice that after a few minutes boiling gives you a couple of cups of cooked rice), for when there is the inevitable gastro-intestinal upset, and the vet recommends a bland diet of cooked chicken and rice. We have a dedicated jar of sugar-free peanut butter in the refrigerator for giving pills as needed.
There are all kinds of theories and methods of obedience training out there. I strongly recommend puppy classes for basic manners, and intermediate and advanced if you want to. Your vet or the local pet store may have classes or referrals. What has worked for us is never using hands for discipline. Hands are for love, comfort, tending to needs, pleasure, never hitting or threatening. We use two old metal pie plates (foil has worked too), banged together sharply, to get the dogs’ attention when they are not listening or getting out of hand. Now all I have to do is hold the plates where they can see them, and the barking stops, the jumping stops, and I get the “uh, oh, pack leader has spoken, we better settle down.” Even DH stops what he is doing…
When nipping is involved, and it gets too rough, give a sharp yip of pain yourself to let them know it’s too much. If they are chewing things, take the unapproved thing away with a “no” or “off” or your consistently used command in your pack leader firm but not yelling voice, and offer an approved age-appropriate chew toy, with lots of praise. We have a basket of chew toys and other toys in the family room. The boxers know that’s their stuff, so they go get something when they have the urge to chew. They don’t put it back though…
Be consistent and loving, and the rewards of a good fur friend are beyond compare.