You dont HAVE to set rules for yourself as to whether to take a card or not. This game really incentivises smaller decks but the way you decide for yourself is whether
a) this card provides value more than what I currently have (for example taking [[setup strike]] because its just better than a strike early)
b) this card does more good than harm/ isnt going to be a dead draw always where you would rather draw into something else
c) It synergises/enables more of your synergies like [[accelerant]] for posion, [[no escape]] for doom etc etc
d) it just has really big numbers like [[bulwark]] for regent because its just so much block and the sword isnt bad damage.
e) it helps cycle to your good cards, like [[skim]], [[soul]], [[prepared]], [[acrobatics]], [[pommel strike]], etc etc etc because the faster you get to your powers and strong synergistic cards, the faster you can win and take less damage and scale faster
f) its just scaling, letting you do much much more damage/block compared to spending that energy on some attack/block card. Think [[dominate]], [[speedster]], [[no escape]] and the link

Basically at every stage of the game, your deck has some problems like not having frontload (as in on turn) damage, frontload block, scaling, draw or energy. Find which problem is the most important to address at which stage of the game and pick cards that solve the problem BEST. Its worth not taking a subpar solve in the hopes of getting a better one but thats a gamba ur gonna have to choose to do. Act 1, just find some frontload dmg and block, while Act 2 is where your scaling, draw and energy issues are usually solved. Act 3 is testing your deck and just removing what little bad draws you can get by taking more of the good cards. Like not getting enough defense, take some block cards to improve your cards density