The single most important piece of advice I give in dog training is this: reward what you want. We have a tendency to pay attention to behaviors we don't like (No, Spot! Stop barking! No, Spot! Stop jumping!), and when the dog is behaving the way we want, we have a tendency to ignore it. It's a huge and common mistake. The dog gets feedback that undesired behavior gets attention and calm behavior is pointless and boring. That's exactly the wrong message!
After helping lots of handlers and dogs in group classes communicate better with their dogs, I have a second piece of advice to add to the first: When you're rewarding what you want, make sure you mark it first.
Marking the desired behavior helps your dog connect his action to the reward more easily. It's a way of helping your dog figure things out.
A marker is a unique sound that you make at exactly the moment the dog has done something right, and you always follow it up with a reward (e.g., a treat, a toy, a game, etc.). That sound could be a clicker, which is the heart of clicker training, or it can be a unique sound you make verbally, like a happy "yes!"
Why do I need a marker? If I'm teaching my dog to sit, and he sits, and then I give him a treat, it's not easy for him to connect the treat to the key action (butt on the ground) that I want. There are a million other things going on in his world, so what made the treat happen? Was it making eye contact with me? Was it being in front of me? Was it the hum of the refrigerator? Was it the tile floor? Was it the fact that I reached into my treat bag? My facial expression? The way my hand is on my hip? The fact that he danced his paws a little in anticipation?
By marking the moment of success with a unique sound, you make it a lot easier for the dog to figure out that his butt hitting the ground is what made the reward happen, since you mark at the moment of success each time. So a dog who has been marked at the moment of success and the rewarded five times in a row is a lot more likely to "get it" than a dog who is just rewarded those five times with no marker first.
When you're learning to mark your dog's behavior before rewarding, the clicker has the advantage of being a unique, precise sound. We babble at dogs all the time, so the "yes!" isn't quite as clear as the clicker. However, the "yes!" has the advantage of freeing up your hands. I'll use one or the other, depending on the situation. I like the clicker for shaping truly precise/complex behaviors, like putting the back two paws on an agility obstacle and the front two paws on the floor. And I like the verbal marker for general training when we're out and about and I don't have a clicker handy or a hand free for one.
So as you're looking to develop truly effective communication with your dog, consider adding a marker to the mix. Decide the criteria of what you're trying to teach your dog, mark the exact moment he meets those criteria, and follow up with great rewards. This isn't an intuitive thing for us to do, so it really takes focus and attention on the handler's part to make it a consistent part of giving clear feedback to the dog. But it's absolutely the second biggest improvement most handlers can make to their communication.