I would say Training Your Puppy To Sit is one of the first tricks to teach. In addition it forms the groundwork for many other dog tricks. For instance to train a pet to sit up, prepare some treats as a rewards. I would set your dog on his haunches in a corner, so that he cannot fall either backward or sideways. Therefore they have very little or no space to lose balance. For example keep them from pitching forward by holding one hand under pets chin. I would say with the other hand hold the treat above the nose. Best of all keep repeating distinctly and deliberately say, “sit up.” I would not make them sit up too long at any one time. For instance repeat the lesson frequently and reward dog often with plentiful of praise & pooch treats.
I know with the first lesson they will require considerable assistance from your hand to prevent from pitching forward. Most importantly when they get control of the balancing muscles and understands what you want. For example they will depend less and less upon your hand to keep them in position. I would say you can gradually render pet less assistance until you will only have. I know with constant practice they will sit up well after you set them.
Besides they should be set up against the wall, so as to afford a support for puppies back only. For this purpose after he has been well schooled at this and can keep his position easily, In addition with practice against chair legs, cushions or other objects that afford him less assistance. Therefore until finally the dog learns to preserve his balance and sits up without anything to lean against. I know Training Your Puppy To Sit can be rewarding.