On smaller fittings split the Teflon tape down the middle and wrap tight, the threads will show through the tape and two complete rounds will be enough. Its ok if it laps over the hexagon nut used to tighten, keep it 1.5 to 2 threads away from the end to ensure none contaminates your air system. NPT tapered threads are designed to be turned in three revolutions by hand followed by three with a wrench, leaving two complete threads exposed. After its tight and leak proof remove excess tape with a brass wire
brush.
I do not like liquid Teflon as it is messy, expensive and hard to remove when dry. TF-15 or 'Pipe dope' is more of a lubricant for larger fittings helping with friction during assembly.