I've done a bunch of simple bolt-on for my cars. (strut bars, exhaust, intake)
Maintenance on my cars. (oil change, dif, tranny, brake, clutch, coolent flush, brake rotors+pads)
Changed the shock+springs few times on my integra and coil-over install on my silvia.
Bunch of suspension bushings and steering rack bushing. Extended lugs
Giving mechanic friend a hand with my 5 speed swap on my integra.
Then there's a bunch of random stuff like taking apart bunch of different panels, taking my bumpers off and putting them back on a bunch of times to either paint them or to do some work behind them.
Or just adjusting the idle of my car and installing some Recaros

All of this was learnt from the internet and/or asking someone about suggestions or tips.