Rules or past history

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There's often two competing ways of learning grammar, that comes both in the context of learning the grammar of your native language to write better, and of the target language you're trying to learn.
The first one is based on the rules. You try to learn as much rules as possibles and choose the right way to write the word depending of the rules. Sure, they may get complex and you may need to learn them multiple times.

The other way around is to read, read, read, and try to know the basic rules (because these ones are too much essentials) but then base yourself under your read text in the past: you write the word as you saw others writing it earlier.
What approach would you choose, and why?