Flashing

Leaving the siding joint over head flashing uncaulked — it's the drainage exit for water that gets behind the siding.

The flashing at the bottom of a roof-to-sidewall run that diverts runoff into the gutter instead of down the siding.

Slipping a flashing piece behind each siding butt joint instead of relying on caulk.

Pitching a rough sill with a back dam so water that gets past the window drains out instead of soaking the framing.