Start with a treat in the hand - Raise the hand above the puppies head. The puppy will look up and as a result their bum is likely to go down into a sit. as soon as the bottom hits the floor, click, then release the treat. Throw a treat to one side to get the puppy to get out of position and then repeat.
Once the puppy is reliable at doing this I no longer have a treat in the hand I am raising but still reward every time. At this stage I do not add my verbal cue 'Sit'. I will wait until I am 100% sure when I raise my hand the puppy will sit.
Have a treat in one hand. Allow the puppy to know the treat is there and close your fist around it. Put your closed fist to the ground and wait until the puppy lies down. This takes patience and may take several minutes. The puppy will likely try to steal the treat and paw at your hand. Once the puppy lies down, 'click' then release the treat. Throw a treat to one side to re set the exercise and repeat. Don't add a verbal cue until the dog does the behaviour reliably every time.
Tip: If your puppy is really finding this hard break it down a little and click & release the treat if they lower their shoulders a little (like a bow), after about 5 success like this wait a bit longer for the down. Don't be tempted to push them into a down - some dogs find this a difficult position to learn so it needs to be fun.