For a first go at ribs, use the K.I.S.S method. KEEP IT SIMPLE STUPID!!
Find a rub you like, rub em down, and decide on a temp you want to cook them at. For spares, I'm a big advocate for the 225-250 range. 4-5 hours depending on the size. I've gone as long as 6 hours riding at a solid 225 before on a real meaty rack. Don't over think it your first time out and remember that if you're lookin' you ain't cookin'.
18.5" OTS, 22.5" OTG, CB Silver(Rip), Vintage Coleman Bullet, Pit Barrel, UDS