To start, get some of your puppy's dry food. Put a piece of the food right in front of your puppy's mouth and see if you can lead him around in a circle. If you can, then the pup's food will be sufficient. If not, you will need to get something better like a yummy puppy treat. Once you have a food lure the puppy will follow continuously, you are ready to start the training.
This exercise is designed to create movement from the pup to a posture - not to teach a verbal command - so DO NOT say sit, down or stand while the pup is learning to move to the posture - more on this later.
The Sit: With your puppy standing and with the food lure right in front of your puppy's mouth, slowly raise your hand slightly up and back until the puppy sits. When he does, release the food to him. Troubleshooting: If the puppy jumps up at the lure, you moved it too high and away from his mouth.
The Down: With your puppy in a sit, put another food lure in front of your puppy's mouth and very slowly lower the lure in a straight line to the floor directly between his front feet. If the puppy stands up instead of lying down, you probably moved the lure to quickly down or moved the lure forward away from the puppy. If the puppy remains in a sit, just wait him out until he lies down and then release the food to him making sure the puppy is completely lying down (not just hunched over). Troubleshooting: Practice on a slick surface like tile, linoleum or hardwood so the pup can slide backward easily as he lies down. Make sure you are not dragging the lure forward on the floor. Make sure you are moving the lure very slowly.
The Stand: With your puppy in a down, put another food lure in front of your puppy's mouth and very slowly raise the lure up and away from him until he stands up and then release the food to him. The lure should be raised no higher than his standing nose level or he may sit before you can reward the stand position. Troubleshooting: If the puppy won't get up then get all giddy and swiftly move further away from him.
Training Tips: Once the pup is reliably moving to each posture in the sit, down, stand sequence when you move the lure slowly, it's time to speed him up so begin moving the lure faster and faster a little bit at a time so you always have success. Once the pup is really good then and only then, ADD THE VERBAL COMMAND for sit, down or stand at the precise moment the pup attains the completed posture and not before.
Now start rewarding randomly, not on each posture.
Next, if you are having good success with this sequence, then start mixing it up, i.e., sit, down, sit, stand, down, sit, down, sit, stand - you get the idea. Always keep the total training sessions limited to just a few minutes.