Pick what it does wrong on track. You get the changes in the order a tuner would actually try them — not a list of everything that could theoretically be wrong.
One change at a time, then ride it. Two clicks minimum or you won't feel it. Three clicks is a real change. If you turn four knobs in one session you have learned nothing, and you'll spend the next month trying to find your way back to a setting that was fine.
The settings your bike ran perfectly on — and the air it ran them in. Everything else is measured against this.
After a hard 3rd-gear pull, kill it and coast to a stop. Tan-to-light-brown plug = right. Chalky white or blistered = lean, stop riding. Wet black and fouling = rich. On a 2-stroke, lean is what melts pistons — when you're unsure, stay one size fat.
Your ECU reads air pressure and intake temperature and already trims fuel for density — you are not going to fix thin air with a fuel map. What density altitude actually changes for you is how much power is on the table, and therefore gearing, map aggression, and how the bike will hook up. Fuel/ignition maps are for changing the bike's character — smoother off the bottom in slick conditions, harder hit when there's traction.
Measure rear axle to a fixed mark on the fender, same spot every time. Millimeters.
Clicks counted out from full stiff. Change one thing at a time, two clicks minimum, or you're guessing.
Shorter (bigger rear or smaller front) — tight supercross-style tracks, sand, deep ruts, short straights, or thin mountain air where you've lost power. Snappier drive, more revs, lower top speed.
Taller (smaller rear or bigger front) — fast national-style tracks, long sweeping straights, hardpack. Calmer, less shifting, less wheelspin off the gate.
One tooth on the front ≈ three to four on the rear. Countershaft changes are the blunt instrument; use the rear to fine tune.
Race-pace intervals. Trail and play riding stretches them; sand, mud, and a screaming 250F shorten them.