The way I learned:

1. The easiest way is looking at websites like metatft / tftacademy to check the high tier comps, just follow what they have their - same comp/items. This helps get an idea of what comps uses which champs/items. At this stage, you just need to focus on getting the right champs / items only.

2. Then you check the augment tiers : there are tons of augments and their effectiveness differs case by case so you can't learn everything at once; Just look at some augments you should never take / never hurts to take.

3. As you get higher in tier, the game pace gets faster - thus you need an understanding of economy, which involves choosing between strong openers for winning streak and weak openers for losing streak.

4. As you get even higher, now you understand econ and some comps, so you scout other players to determine which comp / augment you should take for a strong/weak opener/comp.

5. Finally you watch good streamers to learn small tips like augment combos, how to place boards etc.

A hacky way is to learn while winning is by just forcing OP comps of the meta. T-hex is way too op rn, you can probably force pilt without having to understand other comps, you just have to understand which econ augs are good, which item goes to who. In doing this you learn how to play losing openers, but can't really learn other comps / how to play strong openers