There's a variety of factors that make it difficult to suggest a certain "pace" at which to puff your pipe...
The pipe itself - it's bowl size/depth, the tobacco and it's cut/moisture level, how the tobacco is packed in the pipe, etc
Each pipe may vary slightly and tobacco may vary a bit, just experiment with what "works" for you and ENJOY the smoking experience is all that really matters.
A long, smooth "sip" is how I generally smoke my pipes - with an occasional blowing "out" thru the pipe to move any moisture back down the stem. This also it seems to give some extra oxygen to the burning process. I may also give a half dozen or so puffs that are slightly more quickly paced also if I want to get the "coal" inside the pipe hotter.
Relax and ENJOY is the key to it all...
