I Want To Teach My Havanese/poodle (he Looks Like A Maltese :o)) Some Tricks, But I Don’t Know Which And How

Any suggestions? He’s 3 years old, is it too late?

How Can I Teach My Dog (she’s A Havanese Of 4 Months) To “down”?

I tried the method on the book “101 dog tricks” by Kyra Sundance and Chalcy but it doesn’t seem to work. The method that failed was holding a treat (in this case cheese) and putting it n front of her nose, then saying “down” and lowering my hand to the floor holding the treat, but she doesn’t “down”. What can I do?