I found out the hard way that if you're flat, they're going to be flat. Keep in mind that right now you're TEACHING. They don't know anything. If you're a boring teacher, you're going to lose their attention. Lots of treats, lots of praise. Talk in an excited voice. I stopped giving "commands" so to speak, because the tone was wrong for my dog. I actually switched languages, and got a faster response and more reliable response. I also changed my tone when I changed languages. The faster the response (once they know it enough to be able to do it) the bigger the reward. I come from decades of 'forced' training. It worked, but it didn't make for a happy pup. Stop when the pup is still interested. Multiple short sessions no more than five minutes.
Wrath of Grim z Dragon
"Mr. Grim"- Threaten my handler. I dare you.