You are really doing well with that dog. You praise him. The same is true for your human students. A method that is very helpful is to point out to the class what the student did right. That's an excellent example of appropriate body language.
People really remember that.
It represents high praise from the teacher. You must be careful, though, and not play favorites. This method works best with people who have been having trouble and who get something right. Don't praise unless praise is warranted, but do work very hard to find something to praise. That may seem difficult at times, but it's really not that hard.