Below are the seven rules(that I made up, but are very useful) that you can follow to become the greatest Pokemon Master, which cards, that is.
1. When you make your deck, have at least 25 trainer cards. Many peope lose the game just because they don't put in enough trainer cards.
2. I suggest that you only put one type of Pokemon. So that means if you use grass and fire Pokemon, you shouldn't be doing that. Putting both types is legal, but you'll have too much energy cards, and you will probably come up with the wrong energy cards.
3. If you really want to use two types of Pokemon, then use a colorless type(which can take any energy card), and some different type.
4. Put a few trainers in. Pokedex would be good for searching cards, and Potion and Super Potion will heal your Pokemon.
5. When making a deck, you want to use evolution cards. If the Pokemon you have has three evolution stages, put in four of the basic Pokemon, two evolution Pokemon, and put in only one fully evolved Pokemon. Having more fully evolved Pokemon isn't useful.
6. When you're in battle, don't just weaken your opponent's active Pokemon. Also weaken their benched Pokemon. For exmaple, when your opponent is paralyzed, asleep, or just can't attack, don't attack that Pokemon unless it still have a lot of HP. Now the time to try and knock out a few of your opponent's benched Pokemon.
7. Buy booster packs. Buy tons of them if you really want to become a master. theme decks are good, but just not as good.
If you follow the seven rules above, I'm sure you'll become a great Pokemon Master, with cards that is.