NOTE: This post is a work in progress. Apologies if it is a bit rough around the edges.
Go for full length enclosed outer gear and brake cables to prevent them clogging up with mud and rust.
Use gaffer tape to protect chain stay and cable outer rub
Use Sugru to stop rubbing / vibrating cable
Brasso to decontaminate disc rotor with oil on it.
Use cable ties instead of built incable routing eyelets to get more efficiently cable routing.
On a mountain bike, try the seat higher and saddle fore / aft position further forward to promote ‘spinning’ the pedals rather than ‘pushing’ the pedals.
Use a spirit level app to set saddle level when initially fitting
Sometimes stripped crank threads on hollowtech style cranks can be bolted through and continue to be used which would be fine for local use.
When fitting cleats cleat position at extremes and work your way back
Wear a cycle cap under helmet to soak sweat
Cut worn fingers off old gloves and use as road gloves
If you want to set up a bike well, commute on it and make adjustments over time
Clean chain with rag and lube every ride
Use a pipe cleaner clean next to bottom bracket.
Use a toothbrush to get to hard to reach places.
Clean and relube inside mini-pumps to prolong life