A good way to become an experienced deckbuilder, you should test your deck against as many different types of decks as possible. By using this deck testing process, you can successfully weed out the Pokémon and other cards which really don't help your deck and replace them with more copies of the ones that do. This weeding produces more consistent decks. For an example of how this works, I have provided the decklist for the "Blackout" theme deck:
12 Water Energy
3 Staryu
4 Squirtle
2 Wartortle
16 Fighting Energy
4 Machop
2 Machoke
3 Sandshrew
3 Onix
1 Hitmonchan
2 Farfetch'd
4 Energy Removal
1 Super Energy Removal
1 Gust of Wind
1 PlusPower
1 Professor Oak
Since the theme of this deck is supposed to be Energy Removal, let's concentrate on that theme. To do this, we will replace Pokémon that really don't help the theme and replace them with some that do. Onix and Sandshrew really don't support the theme at all, and each of them is only capable of 10 damage, so we will remove them. We will also remove the PlusPower, since only one isn't really capable of much. Using these 7 slots, we can add in 4 Dratinis and 3 Dragonairs. They are good for a few reasons: They are resistant to Psychic, which the Machops, Machokes, and Hitmonchan are weak to; and Dragonair is supportive of the Energy Removal theme.
Also, since we removed 6 Fighting Pokémon and added 7 Colorless, we want to add 4 Double Colorless energies in place of 4 Fighting Energies. Although Hitmonchan does not directly support our theme, it is one of the most efficient Fighting Pokémon, and Machoke is horribly inefficient (3 retreat cost, overcosted attacks), so we will remove 2 Machokes and replace them with 2 more Hitmonchans. The Water Pokémon mix is perfect for the addition of another energy removing line: the Poliwrath line. Although this is not one of the best lines, it supports the theme. The Squirtles can be replaced with the Poliwags, the Staryus can be replaced with Poliwhirls, and the Wartortles can be replaced with Poliwraths. This produces a good, clean 4-3-2 ratio in the evolution line, which allows for maximum efficiency.
Since we have a large amount of Pokémon already, we can replace the Farfetch'd with the ultimate drawing control card - Bill. I would like to make 4 Bills available, so I will remove 1 Dratini and 1 Dragonair (since we have so many different Pokémon already) and replace them with 2 more Bills. To further the Energy Removal theme, the Gust of Wind will be removed (even though it is a good card, only one is just not going to be helpful enough) and add another Super Energy Removal. We will also adjust the energy mix by adding 3 Water Energy and removing 3 Fighting Energy since the Poliwrath line is more energy consuming than Machops and Hitmonchans.
After the revisions, the deck looks like this:
15 Water Energy
4 Poliwag
3 Poliwhirl
2 Poiliwrath
9 Fighting Energy
4 Machop
3 Hitmonchan
4 Double Colorless Energy
3 Dratini
2 Dragonair
4 Energy Removal
2 Super Energy Removal
4 Bill
1 Professor Oak
These revisions produced a tighter, more focused deck by removing cards that were not valuable to the deck theme and cards that were inefficient. Even with the revisions, however, the deck is not perfect. To help increase the deck's power, you would play more matches (preferably against varied decktypes) and trim the deck down even more by adding cards which work against a multitude of decks rather than only certain decks.
