First we must start with what kind of dog you have. All dogs come with the basic starter pack of genes; they instinctively like food and/or social interaction.
It is critical that you know what is rewarding for your dog; does he prefer food treats*, stroking, or a game of fetch, or a tug on a toy?
After all, you are expecting an appropriate salary from your employer for your performance and so does your buddy. When we look at the wolves, we see that their salary is the prey they hunted. Dogs should not hunt; we have to redirect this instinct behaviour to an appropriate occupation. If they perform really well, they should get a really good salary, too: Their reward.
Dogs learn the right way to behave by experience. What they are rewarded for, they do again, and learn by associating what they are doing at that time, with the reward. This means the best learning takes place if we can reward the dog when it performs the behavior we want. One second afterwards may be too late.
Fortunately, there is a way we can extend the timing of the reward. Add a praise and the cue as you give the reward – “nice sit”, “good down”, etc. By repeating the cue you strengthen the association to the behavior.
Do not use “good boy” or “good girl”. Additionally you may use the clicker. The tiny movement of your finger is even faster than your voice, but your dog needs to know the clicker.
You have to be absolutely confident, that your dog knows the cue. “Sit” means sit, regardless of anything else, whether you say it quietly, or firm; whether you are wearing a hat, or stand on one leg; whether you are in the living room, or at the dog park. At this point you can add the release trigger.
Why a release trigger? Most dogs leave the position they performed as soon as the reward appears. That is not the goal. A click or “nice sit” does not equal “do what ever you want to do”.
E.g. you want to train down and stay. Your dog performs the down perfectly. You stay with your pup, click and/or praise for the down, then add the release command “free” or “off you go” and encourage him to leave the down position.
Now he learns, that he is only allowed to leave the position after hearing the release trigger. Next, you ask for the down, click and/or praise, go a few steps away, click and praise again. If your pup still is in the down you go back to him, say the release command and reward.
Start teaching a new behavior somewhere with no distractions, and follow our instructions.
*If you train the “come when called” and the “leave it”, make it something extra special, not just ordinary dry staff. Try white cheese, like Mozzarella or beef heart, cut into small squares. For everything else you may want to use tiny pieces of dried beef liver, so the ants and birds stay away from your pup’s reward.