Well, disciplining/praising your Tamagotchi is difficult to decide on what to do at certain times. If your Tamagotchi has full happiness/hunger and it wants attention, discipline it.
But when its a baby/toddler and wants attention, sometimes give a praise to it, it will give you a training bar.
But if the tama is crying or in a bad mood with its back to you then you must praise it.
In the instructions it says if your Tamagotchi gives a bad present to discipline it, I have done that and it doesnt always give you training bars, but you can do that if you wish.
Some say that if you praise your Tamagotchi intentionally lots, it will start asking for attention more often, keep praising it, then when it asks for attention regularly begin to discipline it and you will get many of training bars.
I hope I helped, if you need further assitance feel free to ask.
//Haze