When your dog knows the release cue and how to sit on cue, put him in a sit, turn and face him, and give him a treat. Pause, and give him another treat for staying in a sit, then release him. Gradually increase the time you wait between treats (it can help to sing the ABC’s in your head and work your way up the alphabet). If your dog gets up before the release cue, that’s ok! It just means he isn’t ready to sit for that long so you can make it easier by going back to a shorter time.
Remember that training is an ongoing process. You will never be completely finished. It is important to keep working on obedience training throughout the life of your dog. People who learn a language at a young age but stop speaking that language may forget much of it as they grow older. The same goes for your dog: use it or lose it. Running through even the most basic tricks and commands will help them stay fresh in your dog's mind. Plus, it's a great way to spend time with your dog.
Just as a child needs a caring parent; an athletic team needs a coach; your puppy needs a leader and a clear social hierarchy. If you do not take up the role of leader, your dog will; and you will end up with an unruly, disobedient dog. Many people try to win their new puppy's love by letting the puppy always have its way. Buckets of affection is a wonderful thing for most puppies, but it must be tempered with respect.