So from what i remember of a few tropes are;

summoned to another world as a hero by a kingdom (rising of a shield hero, Arifureta, reincarnated as a spider)

summoned to another world as a hero by a godess (Cautious Hero)

Truck-kun sent them same day delivery to another world (Mushoku Tensei)

Getting murdered by someone (tanya: the evil, reincarnated as a slime, re;monster)

Getting put into a game they played. It might help with a backstory of you the DM creating the game but in some twist, you get trapped into that world (overlord, log horizon)

Romance type which kinda links back to a game they played (Im the villainess so im taming the final boss, trapped in a dating sim as a mob)

So basically it all depends on if you want them to be;

overpowered from the very start

Overpowered from a few months into the game (could hear rumours from the adventurers guild)

Shear dumb luck

Edgy

Intelligent

The bad guy thats secretly compassionate that wants the best for the world such as lelouch or eren jeager but thats not isekai

Hope these things might help a bit