Always take your puppy out to go potty after he has been fed or after waking up from a nap.
Puppies control their bladder approximately one hour for every month of age. So the younger the puppy the more often you will need to take them out to go potty. Yes that means getting up in the middle of the night a couple times.
Always take your puppy out to go potty on a lead. Potty time is not playtime. And besides it a great way to start training him to walk on his lead.
Pick a designated area for your puppy to go potty.Go to the same spot each time you take him out. Using a phrase like "go potty" each time.
Praise him for eliminating in his designated area.
After your puppy has gone potty you can reward him with play time. Remember potty time is not playtime.
Supervise your puppy. Use a child's gate to block your puppy off from the rest of the house (a room that you are in). If you are not in that room supervising your puppy, then put him in a exercise pen until you are back. Do this until he fully potty trained and done with his teething stage.
After 15 minutes or so if your puppy hasn't gone potty go back inside and either put him in his crate, pen or with the lead attached to you. Wait some time or till you think he is giving signs that he needs to go out. Eventually you will pick up on your puppys warning signs that he needs to eliminate.
Never every reprimand your puppy for having an accident....EVER.
If you catch your puppy in the process of having an accident then use a firm low voice and say "no", pick up your puppy and with a gentler voice say "go potty" and take him to his designated potty area. Reward your puppy with praise and a treat when he eliminates in the designated area.
Don't forget to clean your puppies accident up with an odor eliminator.