Things I work on the most in order of frequency seem to be...
Drive train lubrication —- clean off dust/muck after every ride, lube with light weight but penetrating lube, I use purple extreme.
Spoke and rim adjustment —- buy a spoke key and learn how to use it
Tyres —- pressure and wear, both which I check before each ride
Front and rear shocks —- check pressures every week or so, get serviced when they start to go, about every 6 months.
Headset and bb bearings —- check regularly for wear and movement
Gear cables and shifting —- make sure shifting remains quick and accurate
Suspension bearings —- I don’t really check this, rather I can feel it going during a ride
Brake pads and fluid —- keep on eye this, pads can last a week or a year depending on conditions and use.
I’ve never had to adjust hanger alignment.
Given all that I don’t keep my mountain bike that clean as I’ve found it’s dirty within 2 miles of hitting the trails.
Number one tip, always carry a multi-tool, pump and spare tube.