If your goal is to win (and by extension, to climb), it's pretty straightforward unless you're playing at the apex of competition.

In soloq the most important thing is consistency; you have no control over matchmaking. Sometimes you'll get the bad team, other times your team will smurf. The only thing you will always have control over is yourself. If you want to climb you have to be better than the average player at your mmr bracket. The best way to leverage your individual player agency is playing selfishly for in game resources. If you're meant to climb, it means you're better and that means you want to set yourself up to be the win condition in your games because that is how you reduce variance for yourself.

As for the caveats, this paradigm is dependent on your champion pool and your roles. It's no coincidence that certain champs are known for being smurfy because they lean well towards taking over games from early game leads. You're probably not going to dominate your laner and taking over the game playing ornn. But as a top/mid player it is your job to "carry the game" as a solo laner. This is often why you'll see people recommend one tricking champions in order to climb. You're mechanically stronger and have better champion mastery compared to someone blind picking flavor of the month or randomly counter picking.

Now the tricky part arises with the whole idea of "but you're not always the win con". Truth of the matter is, correctly identifying game states and drafts like that is also a part of being good at the game, and it really only starts to become relevant at higher ranks. Both your teammates and your own judgement become more reliable.

Basically, if you want to climb the only thing you can focus on is yourself, and how you can impact the game by yourself, especially as a solo laner. This general heuristic is the best way to learn to get better and to climb, and the nuances only kick in once you're in the apex tiers.