Sit is a basic command that all dogs should learn. There are 2 ways to teach it, depending on your dog's personality. If your dog loves food and is "soft" then you should probably use the first method, but if your dog doesn't care for treats or is a little more strong willed, you might want to try the second method.
Treat and lure method:
With this method you will get a treat and show it to your dog and raise it above his head, and lure him into a sit position with the treat, and once he is sitting give him the treat. A little push on the butt can help. Start saying "Sit" in a firm clear voice. Once he starts to get it give a treat every other time. Soon you will just have to use your hand, to give the command, or say sit.
Pressure method:
For a dog that is stubborn or strong willed, you will need a collar and leash on your dog. Say "Sit" and pull up on the collar, and push his butt down, until he sits, and praise. Repeat until he does it more and more willingly. After a while he should sit whenever you tell him to.
Down -
Down is another basic command. There are also 2 different ways, treats and pressure.
Treat and lure:
with your dog in a sit position, take a treat and let him smell it and lower it to the ground slowly with your dog's nose following, until he has to lay down to get the treat, as soon as the elbows hit the ground, give him the treat. Repeat until he lies down when you touch the floor. Say down as you lower your hand.
Pressure:
With your dog in a sitting position, take his front legs and pull them forward, and say "Down" and pull his legs on the ground so he is laying down. Praise. Repeat this until he goes down easier and easier. If he resits you pulling his legs, try pulling down with the leash, and even stepping on it if you have to, and then pull the legs forward. Once he starts to lie down, try just touching the floor and saying Down.
Stand -
Teat:
With your dog sitting, take a treat and pull it forward so he has to stand up to get it. Give him the treat and praise. Repeat this until he stands when you move your hand away from him. Start saying "stand" as he stands up.
Pressure/leash:
With your dog sitting, pull on the leahs or collar so he has to stand, while saying "stand" and if needed, tickle or apply pressure under his belly to get him to stand up. Praise. Repeat until he stands up at the touch of his belly or the command Stand.
Stay -
Teach this with your dog's collar and 6 foot leash on. There is generally one way to teach Stay. Put your dog in a sit position. Stand on the right side of your dog. Place your palm in front of your dog's nose, fingers pointing down, and say "stay", and walk in front of your dog. If he gets up, put him back, use the hand signal, and command "stay" and move in front again. Praise/give treats! Go back to the right side of your dog. Command Stay and use the sang signal again, and walk in front of him again, praise, and then walk to the other side of him. If he ever gets up, replace him and use the signal and command. Repeat by slowly walking all the way around your dog so he won't move. When he stays with you walking closely around him, Start taking a step away from him and doing the same thing, step by step walking around him. If he gets up, replace him and say stay and use the hand signal. Repeat this until you can stand a full 6 feet away(the whole length of your leash) and walk around him with him saying. You can contunue the distance with a longer leash or string.
Come -