To start off with, its a good idea to have a core identity (not Identity) for your deck. What does your deck do?
Usually the identity is tied to your Identity, but not always. Sometimes many different runners can use the same flavor of deck and do similar things to the corp.
A general idea behind a Reina deck might be: Tax the corp by causing his ice to be very expensive. When the corp cannot rez ice, I can steal any agenda I want.
Based on that principle, we start to include cards that benefit that plan. Xanadu. Hernando Cortez. Cards that force the Corp to rez ice or rerez it. Emergency Shutdown, Forged Activation Orders, Crescentus.
From that initial principle, we also find our win condition. Are we trying to score 7 points? Mill the corp? A bit of both? If the corp cannot rez their ice, Keyhole might be a way to trash their helpful cards and put agendas in archives and run the corp out of cards.
We also need to pay for our plan. Sure Gamble. Daily Casts. Liberated Account. Temujin Contract.
We also need to be able to break ice or otherwise get into servers. Paperclip, Eater, Faust.
Once you have settled on a plan for what you want to do, start condensing to the core elements of the cards you have selected. Maybe you dont want to have to run HQ before derezzing ice, so drop Emergency Shutdown. Maybe you dont want to derez ice at all. Remove Crescentus and FAO. Maybe you want to trash ice that they cant rez. Put in En Passant.
Find happy mediums for what you want to do, then test them out. Eventually you will get a feel for how certain cards play and either enjoy them or not. You will also get a feel for why the majority of players use particular cards like Ive Had Worse.
There is no shame in building a deck you have seen off the internet and then trying that out. You may find a deck you really enjoy or find a way to improve it or tweak it to your preferred style. This also gives you help since you can start with a solid foundation without having to second guess all 45 cards in your deck.
Hope that helps!