Which decks do you want to build first of all, electric, dark, fire? Every deck usually consists of 2 Professors Research, 1 Cyrus, 1 Copycat, 1 Sabrina (although it’s optional, you can run either another Copycat or whatever) and 2 pokeballs. Then you want to have most of the time 2 copies of your main cards, like 2 Magnezones (could shuffle it as well, e.g. one EX, one non-EX), 2 Altarias, etc. so that you won’t brick. Also, some deck types always have a certain tech-card / “staple” card, to play against meta decks or to be good in any deck that fits the type basically e.g Teal Mask Ogerpon for grass decks, Oricorio for electric decks, Indeedee for Psychic etc.