Almost every dog trainer and dog training book advises us that we should pick simple commands and be consistent, but we all know each and every one of us, trainers included, have violated that rule. We're human, of course! Humans are taught from the beginning to "use your words", to use the adjectives that make us human, to use words creatively to get our points accross. Words, words, words! Not only do we LOVE adjectives but we also love to use our synonyms. We love to word swap! Well, we need to understand that a dog just doesn't understand the use of synonym swapping or correct adjectives or verbal nuances. Dogs just speak dog.
It really is a wonder that our dogs understand us at all. Dogs actually live and cohabitate with us as if they were living in a foreign land.
Think about it. When you visit a region where you don't speak the language, what do you do to get your point accross? You use hand gestures to signify what you mean. You use your facial expresssions and other forms of non verbal communication. Well, guess what. You just figured out the key to dog interaction.
Raising your voice if they don't understand you will just cause them to tune you out. You might as well not be saying anything.
So remember, simple repetition but most of all PATIENCE.