Sit & down
The commands 'Sit' and 'down', are useful for a range of situations. when you have to leave your dog when doing agility classes or when you need to get something and want your dog to remain where they are. Along with the Recall, this is one of the key training sessions for you and your dog - if you want to have any chance of a trained and well behaved dog anyway.
Technique :
If by any miracle you have a dog that does this anyway - then don't bother reading on. Do not be daunted by any aspect of training and remember that much of it is repitition. Start by holding a treat in your hand and present it to your dog just above it's nose and motion straight back toward its tail. Hopefully this will produce a sit from your dog as he/she tries to maintain eye contact with the treat. When it does (assuming), say "Sit" and then reward with praise and the treat that your dog was eyeing up so carefully.
To begin the "down", work in much the same way as the "sit". So offer the treat and then drop your hand to the ground between it's front legs repeating "down". Hopefully the dog will follow the treat and there you have it! Should your dog simply move it's head in a bowing action to follow the treat, hold the treat until your dog relaxes and drops it's bottom. When it performs say "Down", then reward.
With both behaviours continue to work until your dog readily performs what you asked. When you are more confident and your dog is doing it more readily, then move on to the garden where there are distractions aplenty. This will ensure that you get more attention, however bear in mind that with a puppy, you will need to keep in mind it's short attention span. Above all keep your training as fun as possible and try not to show any frustration to your dog.