Gathering all the info you can get your hands on is the best way to get the a/f right. Plug readings, wideband and/or narrow band, and some sort of data recording. Plugs get you in the ball park. wideband gets you what your a/f is, and narrowband tells you what a/f your engine "likes". Putting to much faith in a wideband can be very misleading... especially if you are chasing a number instead of listening to your engine... Different engine conditions(load/RPM) will require different ratios.