I'm not sure what type of smoker you have, so the following advice is for electric with water pan, or could be used for WSM with water pan.
Like a lot of the OTBS crew here I get asked to do ribs for different functions, the next is my son's wedding rehearsal dinner 35 people and I will be serving ribs. I do mostly Baby Backs because that is what our favorite guest (my mom) prefers at our parties. The rub I use is a modified version of BRIU. I do the drying out of brown sugar in the oven and it is combined with my rub which I apply after I put mustard on usually the night before or at least 12 hours. When I am preheating my smoker the ribs are dusted again with rub but this is a lighter coat. When the smoker is ready, in go the ribs. While the 321 or 221 or 11111 is a general rule of thumb, there are variables that affect those rules. (Outdoor ambient, is your smoker insulated, can your smoker easily maintain 225º, different size loads in the smoker, etc, all can have an affect on the timing. The key to tender ribs where the meat comes off the bone clean with a slight tug, the ribs are not just falling apart when you lift the rack, is how tender is the meat at the different stages. In the first cooking stage, you are paying attention to how much meat is pulling away from the tip. If the meat is 1/8" and you smoked 3 hours, usually the ribs are still not at the right tender stage, 1/4" to 3/8" is good, 1/2" is too much and the ribs will be over cooked if you do another 2 hours in foil. Personally I do not spritz because I want to leave that hatch closed, no peeking no spritzing, each time you open the hatch it will affect the cooking time, If you own a wood or charcoal smoker with no water pan, then spritzing is appropriate to keep the meat moist.
When you have the right pull back, and it is time to foil, spritz and put some juice in the foil, the meat will steam in the foil and get tender. 3/8 to 1/2" pullback at the end of the foiling stage should be a nice tender rib. The final stage depends on if you will serve the ribs right away or if you are waiting several hours.
When I am cooking for more than our immediate family, the ribs will usually be smoked and done 3 to 5 hours before. So for the final stage it is really a two part process, 1st I open the foil packets and sauce the ribs, then add another layer of heavy duty foil. ( My BBQ sauce has honey added using a 3 to 1 ratio, 3 part sauce 1 part honey, heated and mixed, brought to a simmer for 5 min. I make sure the sauce is warmed up before applying to the ribs, this is a light coating, more for flavor enhancement while they are resting in the packet. I usually put two rack per packet, cover with heavy foil, then with plastic wrap, the paper towels, then plastic wrap again. Next I put them in a ice chest that had hot water in the chest for at least 15 min with lid closed (thus heating up the ice chest). A old towel is placed on bottom and the ribs are added, Newspaper to get rid of air space, and finally after all racks in covered with another towel ( I put the towels in the dry for about 10 min). I seal the ice chest. When ready to serve hours later, the racks are opened an put on a open bbq grill low heat for final saucing which get that rich glaze you are seeking. The ribs usually are so hot they are hard to handle with bare hands, 9 out of 10 times they have the correct tenderness. If a rack is not tender enough it stays on the grill longer without adding any sauce until the end, or it will simply burn and blacken that rack of ribs.
If I plan on serving shortly after the 2nd & 3rd stage, sometimes I will glaze on an open grill, some times I will just add the sauce and glaze in the smoker.
I believe the holding in ice chest is a better tasting more tender rib. On the 4th of July unknown to me an unknown guest at our 35+ party told the friend she came with that the ribs I cooked were some of the best tasting she ever had, ( I was then told she was a local restaurant critic, you can imagine how elated I was). I mention this because I know after years of using these methods I get a lot of compliments, and should be of help to you. (I should add that the ribs I had for the 4th were some of the best looking ribs I ever bought, lots of meat & fat marbling.
I am not telling you all my tricks, I have learned a few things that are either particular for my smoker or I believe enhance the flavor just slightly to add another dimension to what someone might taste.
A lot of great info has been shared in this thread, I think you have enough to turn out some awesome ribs.......