3-2-1 is a basic guideline for rib cooking. Barebones it means to cook ribs 3 hours, wrap in foil and cook another 2 hours, unwrap and cook another hour.
This basic info applies to spare ribs, for loinbacks(babybacks) times will need to be reduced.
Now for the straight poop. "3" doesn't mean anything. Variations in pit temps, particular cut you're cooking type of smoker you're using etc can really play havoc on this first phase so you have to watch the ribs.
The indicator of when to wrap the ribs is watching for the meat to pull away from the ends of the bones 1/4"-3/8". When this happens its time to wrap 'em up.
Use heavy duty foil for wrapping and use caution not to pierce the foil with the bones. I cook the ribs meat side down while in the foil, and always spray the ribs with some liquid (apple juice is a great place to start) before sealing the foil.
Cook for 2 hours in the foil (a bit less for BB's). A good indicator of when to unwrap is to put on gloves and lift the wrapped ribs in the center, when they're quite flexible and both ends droop it's time to unwrap. To get a feel for this lift freshly wrapped ribs and see that they're still fairly rigid.
Unwrap the ribs and cook another hour. This is when you want to use sauce if you like "wet" ribs. If not using sauce, check the ribs every 15-20 mins (peek quickly to retain heat) and spray or mop when the surface looks dry.
3-2-1 isn't the only way to cook ribs, but its a really good way and an excellent starting point to develop your own technique.
---Whoops Scott beat me to the draw...oh well..here's mine anyways---
There are a bunch of post on the topic, but here are the basics:
3 hours of smoke with just a rub, followed by 2 hours wrapped in foil maybe with a bit of juice added(apple works nicely), followed by another hour of smoke.
The times may need to be slightly adjusted depending on the rack you are smoking (baby-backs need slightly less time, large spare ribs maybe a little longer)
During the first 3 hours, you are adding the smoke flavor and looking for the meat to pull back slightly from the bone ( a quarter inch or so).
The 2 hours wrapped in foil is essentially braising the ribs, completing the cooking and tenderizing.
The final hour is when you would sause the ribs if you wish. It helps dry the ribs a bit (they will be falling a part a bit too much sometimes when you take them out of the foil). If you prefer a dry rib, you can add a bit more rub at this time....
Wet or dry is a personal preference...I like to finish with a bit of sauce myself
There are other methods, but this one hasn't let me down yet :D
WOW. Hey Thanks a lot guys. I am really getting into this. I think putting melt in the mouth ribs on the table is an art in itself. I have seen a lot on the TV about it but all they tell you is how good they are but never how to cook them.. Thanks so much.. Hey roksmith. I was born in Bellevue Ohio and have serious thoughts about moving back to my roots. 66 years is a long time to be away from home.. Thanks again..