Most MOT failures are simple things anyone can spit.

Tyres and bulbs are super simple to spot and should be checked a lot more often than annually

Suspension making a noise over bumps? No don’t worry about getting your Haynes manual, take it along to your local friendly mechanic as it might be something dangerous like a snapped spring

Brakes spongy or making strange noises? Maybe don’t wait for the MOT to find out if you can stop properly

Windscreen broken, wipers making a smeary mess or washer jets soaking the cyclist behind you? Otherwise known as “CANT SODDING SEE OUT” - maybe that should be sorted before the MOT too.

Steering making a groaning noise and power steering fluid below the minimum? Gee, maybe let’s not wait for 11 more months for an MOT tester to tell us it’s dangerous

The seatbelt in the back that won’t retract properly? I wonder if it’s a good idea to fix it before putting someone in that seat….

Like I said, the vast majority of MOT failures are preventable by simply paying attention, doing some basic checks yourself and addressing problems as they arise. No, you don’t need a Haynes manual - those are for if you want to fix the problems yourself.