Maintenance

Chain lubing – interval, how, use of rear stand, cleaning chain
Tyres – wear markers, pressures
different types of bike have different service intervals (e.g. changing the oil, changing spark plugs) – refer to your user manual

Modifications

tyres – which sort? sticky (better grip, less kms), hard (less sticky, more kms), wet weather tyres, track oriented tyres (best grip, substantially less kms)
rearsets – important to adjust height at which legs intersect tank = grip and control, comfort, particularly important for very tall or very short people
adjustable levers – feel and adjustment
adjustments to suit individual – clutch, levers, gear shifter, brake pedal, suspension
sprocket size changes, but need speedohealer if speed not read off front wheel
crash protection – oggy knobs, swingarm sliders/spools, front fork sliders, engine covers
braided brake lines