How can I teach a grown dog to sit?

Hey there fellow dog owners. I adopted my dog a few months ago when he was already five years old.(human years) He's probably the most adorable dog I've ever met and loves affection, though, the older owners have never taught him to sit or do anything else, other than coming when you call him. Is there any way that I can teach him to sit, now that he's a grown dog? Will it be hard? I'm talking about a male yorkshire terrier.

Thank you in advance, it'd be really awesome if I can teach him.

Have you ever thought about using a treat to do it? First, get down on the pet's level if possible by crouching down, and then take the treat and guide it downwards and say sit gently but firmly to the pet. That is how we learned to do it in class.

The treat helps to guide the animal to do the actual task. You can use a favorite toy to do it as well. I hope this helps!

You should maybe start with teaching your dog how to behave on a leash, if he has never been taught any behavior manners at all. Once he is learning to walk politely on a leash, he can be told to sit, when you stop walking, and pull his head up with the leash, and he will probably sit right down. Then you can pet him, and reward him for sitting, and soon he will understand the command to sit when you tell him to do that, and will automatically sit when you have him on a leash and stop walking.

Always be sure to let your dog know when he has done what you are teaching him, even if it is just a pat on the head, and a verbal "good dog !", to let him know he understood and did what you wanted.
Most dogs love to please us, and will try very hard to do the right thing once they understand what you are teaching them.

Hmm, I'll try doing what you both suggested. I think I'll have to start off by teaching him how to behave, yes, because when I walk him, he's like a powerful boat pushing a water boarding board(me). Apparently I'll have to search for a good treat to use though, since I cannot use his favorite toy because he'd just go and take it from my hand, and food, well, he isn't the kind of dog that starves for food. As I said in some other thread, you can even drop a stack of meat that he wont care about it. He'll just stay sat, looking at it while we bend down picking it from the ground. I'll give it a try and update this thread afterwards with the result.

Thanks for the advices.