Well, you need to analyze it, then. There must be a good balance between pokemon, energy, and trainers. If you have too little pokemon, then you're almost guaranteed to lose the game. The same goes with energy.
Trainers are a different matter, but they are extremely useful in the game.
Once in a while, there comes a deck that arrives at a tournament that seems to beat just about everyone there. It is very well balanced, and employs a creative use of the cards. I will write down some of the decks I've seen that can do this. Here they come. Note that some of them are taken from PoJo's Magazine.