The way you train your Tamagotchi will affect how it will grow up and how disciplined it will be (determined by the amount of training bars). To earn training bars, you should praise it when it does something good, but give it a "time out" if it refuses to do what you're asking it to do.
Playing games does'nt usually raise those skill bars, I would think.
Playing games earns your Tamagotchi points and helps it lose weight.