As it takes time to build metalsmiths, I tend to take Navarre and Aragon quite Quickly if I play the French (who don't have Iron otherwise): this to have two well developped Iron Provinces. Having Castille and Leon is a bonus (IIRC thet both have Iron also).
As a general rule, I try to get at least one metal province quickly. And furthermore, if there's no trade goods, and not that much farming revenue, you're not tempted to buil merchants and farms, so you're teching troops up quickly!
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