How Often Are Maintence Spankins I Put Plugs Only In My 1994 Jeep Back In 2006. How Often Do I Change Them And Should I Do Any Other Maintence?

I put plugs only in my 1994 jeep back in 2006. How often do I change them and should I do any other maintence? - how often are maintence spankins

How do I know when to tune your Jeep