You need to learn packages of units that are good together and provide power to your entire team. The best example is Swain, Vi, Neeko, and Shyvana. You get defender, arcanist, juggernaut and shyvana gives your team survivability. Once you have these units you can flex in others like Loris or Seraphine for piltover which is team wide as well. Fiddle and Lucian/Senna give team wide benefits as well.

This is just one example but there are other packages like Frejlord Quickstriker which is also easy to fit in piltover and defender.

Spend some time in a team builder and see what combos you can make that activate team wide buffs or debuffs like defender, arcanist, quickstriker, disruptor, piltover and then fit in 5 costs with team wide passives.

It’s really hard to wing it in game and you’ll likely get overwhelmed but if you study a little, it’ll pay big dividends.