One of the toughest parts is figuring out which circuit you are on while cruising (let's say 30_70mph or so). As mentioned, once you know which circuit you are on, then you take allot of the guess work out of the tuning.
When you are out cruising, take notes of the a/f reading at different steady cruising speeds (ref: 30/40/50/60/70mph) then when you make a tuning change, write down the new a/f reading at these same speeds. This will show you exactly where your change made a difference good or bad.