Building movesets comes from battle experience, but after a while, you know what works and what doesn't.
In GSC, Curse was the absolute god of all stat boosts. Slap it on just about any physical attacker, and you were set. Several other variations came: cursing psuedohazers, for example, but it mostly ran around the same theme of stat boosting, and then hanging on to those boosts for as long as possible.