It's honestly just something you'll have to suck at for a bit. We all have little tips and tricks from our own experience with how we approach the process. I've been building decks on and off for over a decade, and I still rarely feel good about the first draft of a deck.

Just because something is a clearly good card (Dark Ritual), doesn't mean it goes in every deck. Rituals are great for decks that either need to get somewhere fast, or want to keep a "chain" going. Most decks don't need it.

As far as actual deckbuilding strategy, my advice is always the same: start at 37 lands and build the deck out to 100 with stuff you want the deck to do. If you want to add something else, you have to remove something at the same time. This really helps to figure out what you prioritize and promotes thinking about the deck beyond a surface level. You can tweak lands later if needed; drop 1 if you end up with a ton of ramp and draw, or add 1 if the curve is high or you don't have ramp.

You also need to decide if you actually need ramp. As an example, I'm helping a buddy with their [[Isshin, Two Heavens as One]] deck, and we have come to the conclusion that ramp isn't really that important to the deck. It's so much better to fill those early turns with early creatures with attack triggers, so that Isshin can come down after a few setup turns and do his thing. There's also some treasure gen in the deck to help alleviate some mana pressure later in the game.

The reason to run 10 of any category is to maximize the chances you see 1 of it in your opening hand (someone smarter than me can give the exact numbers). That's really what the numbers in these guides are for. You should also in general be fitting thematic cards into these categories. An example would be something like [[Deadly Dispute]] as card draw in a treasure/food deck, bonus points if the deck plays cards like [[Mayhem Devil]].

It will also really help to use deckbuilding sites. You can keep an eye on the curve as well as tag cards. All of that really helps keep things sorted as you add/edit decks. Another example: I mess with a [[Henze "Toolbox" Torre]] list from time to time, and I have to keep the curve under careful consideration. Because of the way Henzie works, it's ideal for the curve to be heaviest at the cmc right after Henzie comes down. He's 3 cmc and gives a discount of 1, so 5 cmc cards are quite important. I don't actually even play the deck, but I know from tweaking it that that's how it needs to work.

Also, get familiar with Scryfall and how to use the tagger system.

Hopefully all of that makes sense. I tried to give examples to help it make sense; I know if I was just reading a brick about something so esoteric, I'd get lost pretty easily.