Most first decks fail for the same reason: too many good cards and not enough of a plan.
Start with a ratio
A reasonable starting point is roughly 15 Pokémon, 35 Trainers and 10 Energy in your 60 cards. Attacker-heavy decks that need multiple Energy per turn shift towards more Energy; consistency-focused decks lean harder into draw and search Trainers instead.
Pick one plan
The single biggest mistake in deck building is trying to support two or three strategies at once. Decide how you intend to win — a fast aggressive attacker, a stalling Energy-denial plan, whatever it is — and cut every card that doesn't push towards it, no matter how good that card looks on its own.
Fill gaps with singles, not boxes
Once your deck's shape is clear, singles are the efficient way to finish it — no point opening packs hoping for a specific Rare like Armarouge when you can just buy the one you need.
Frequently asked questions
What's a good ratio of Pokémon, Trainers and Energy in a 60-card deck?
Around 15 Pokémon, 35 Trainers and 10 Energy as a starting point.
Should a first deck be built around one strategy?
Yes — pick a single win condition and cut anything that doesn't support it.
Is it better to build from singles or start with a theme deck?
Start with a theme deck, then move to singles once you know your preferred strategy.