A good set of spark plugs in a vehicle or any spark plugs for that matter should last for 50,000 miles to as much as 100,000 miles before needing changed.
Some spark plugs might even last as long as 150,000 to 200,000 miles.
It's always recommended to change out spark plugs every 50,000 miles to 100,000 miles as regular preventative maintenance.
As spark plugs ignite the fuel mixture they eventually wear down the tip and then they lose their ability to ignite the fuel and air mixture properly.
Bad spark plugs or worn spark plugs can cause hard starting, engine misfires, increased fuel consumption, loss of engine power etc.
I change my spark plugs out every 100,000 miles which is between every 7 to 10 years depending on how much driving I do.
After 10 years I change the spark plugs regardless of miles because a new set of spark plugs are pretty cheap.