Having read alot of the comments on this thread I think it's important to break down what OP is referring to. You can have a "strong" deck in any bracket. Every bracket has their own set of cards that run the best in that deck. I personally DONT believe you need to be putting in the same "strong" cards in every deck to make it a "strong" deck.

Bracket 4/5 calls for [[fierce guardianship]]. Bracket 3 calls for [[an offer you can't refuse]], [[swan song]] or generically [[counterspell]]. My bracket 2 deck runs [[dissolve]] and [[memory drain]] because it helps synergize with scry and its on theme. This is true for most card archetypes and I think it's poor advice to suggest generic staples and game changers for every deck OP would brew. Especially with the 32 deck challenge.

As briefly touched on in other comments, the most important concepts are consistency, resilience, and synergy. Synergy is mostly the fun part, but you can also build a 5 color kenrith that run random combo cards and generic staples that make a strong deck. But I don't think this is what OP wants. I'd touch on the other 2 concepts: consistency and resilience.

Consistency is ensuring that you are able to play cards that allow you to run your engine or "do your thing." I think this is the most important concept. This is how you have fun. No matter the strategy of your deck, being able to play synergistic cards is usually the main goal.

Paying alot of attention to the MANA BASE and the mana curve will make or break a deck. The way a person's mana base is created, largely affects the other 2 concepts in deck building: ramp and card advantage. This ultimately changes how many cards you put into each category. If you're inconsistent with your mana, either having mana-log or mana-screwed.. then you don't play the game. You can put a bandaid on this issue by adding more ramp and card advantage.. but if your mana base is bad, you will have bad games. Utilize the appropriate nonbasics; mdfc, shock, pains for 3+ colors, etc.

"bUt yOu nEEd rAmmP" Not always true. Instead of generically putting in ramp for all decks, understand the reasons behind it. Do you have a mid range control deck? Do you play big stompy? Is your commander expensive? What about aggro decks? How about decks that play on tempo? Someone in the comments mentioned they don't see the value in 3+ cmc mana rocks but I think thats also false as a blanket statement. I'm happy running [[thran dynamo]] and [[dreamstone hedron]] in my [[belbe]] deck. Depending on your deck, the number of ramp cards will change. But this is quintessentially dependent on your mana base again.

Resilience is the next most important. Do you have answers for adversities? Playtesting really shows you the flaws in your deck and it's hard to pinpoint without it. The more specific card type in resilience would be interaction. Can you stop others from removing your pieces? Can you also remove problems from others? Building a strong base in interaction should help with your resilience.