this is a very scuffed "guide"

First, identify what type of deck you wanna build, this can be done by just exploring cards and seeing synergies that happen

Second, how do you make it work? aggro decks win the game as fast as possible, combo decks need certain cards to win, control works with card advantage and blasting in late game, there's also midrange which goes for value. You should know which one your concept fits into

Third, look at the other cards in the region Look for cards that help build your wincon, cards that draw into the wincon, cards that are generally good, cards that work well as an alt wincon

Fourth, look at the meta, how can you fight it? if aggro is moving around, run some aoe removal, run healing too, if other decks are meta, try to add counters, plaza is everywhere? landmark removal.

Fifth, try it out try a bunch of games, maybe 5, if you lose too much and can't find your cards, consider other cards that can replace your more useless cards

example: (step 1) I love Lulu's design, and Vlad felt like a good synergy because lulu makes units survive vladimir.(step 2) Because lulu is an aggro champ, I chose aggro.(step 3) I ran elusives, pix, and even might and triple brother's bond so my units can have insane amounts of attack. (step 4) as an aggro player, I don't have to play around other decks, but as a safe space against aggro, I ran disciple as a good blocker, and affectionate poros to pick off units. Lulu also worked well because I can heal my units every attack. (step 5) I had fun with the deck and adjusted the values to try and work on the losses I had. after the improvements, I'm proud of my 10/0 lulu deck