JRA, what temp are you cooking at? How much wood are you using? What charcoal are you using? All of these things can affect your smoke ring to a degree. The ring is a reaction that happens up to a certain temp (of the meat) which if I recall correctly is about 140 degrees. If your ribs go on cool/cold, this will help. If you add the ribs before the cooker is up to temp (I cook ribs around 240), that will help. Possibly more wood/smoke will help, but you need to be careful to not over do it.
I stopped chasing the ring a while back, as I don't think it adds to the flavor any. Sometimes I get a good one, sometimes not much at all. Tweak some of the variables above to see what works for you.
Rich