Some corrections and additions if somebody would apply them please, will add anything else i remember as and when. 
Front fog lights are not a testable item. Plate lights should come on with side lights. Indicators must flash orange.
Dash warning lights must be seen to come on and go out again when you first turn the ignition on, if you remove the bulb it won't pass.
Removing airbags is dangerous, it's not a good idea to muck about with them and if you do then follow the manufacturers instructions to the letter. If the airbag light is on or flashing it's a MOT failure.
DT brakes are perfectly adequate if properly maintained, if they're not providing enough braking force it'll be down to an issue with old brake fluid, air in the lines, sticking pistons and/or sliders, or cheap/contaminated pads. With the drum brakes you would be better off cleaning them out completely and servicing the mechanism, else they'll seize up again in fairly short order.
Make sure your washer jets actually put a decent amount of fluid onto the swept area of the windscreen, no good having fluid if all your washers point at the pavement lol.
There aren't two horns, one is the siren for the alarm system and completely separate. If your horn doesn't work, get a friend to hold the button while you give the horn a few slaps, often this can dislodge any dirt blocking them and solve the issue. Try giving the plug a wiggle if this doesn't work, a lot of electrical problems tend to be fairly basic issues such as corrosion causing a poor connection etc.
Seatbelts mustn't be frayed, must release under tension and must retract fully, mounting points must be secure. The seat backs should lock in the upright position and be securely affixed to the bases. Any rust within 6" of the seat bases or seatbelt mounting points will fail.
Wing mirrors should be secure, if it's taped/glued back on and doesn't take much to knock off they will most likely fail. You must have at least two working mirrors, one of which must be the os wing mirror.
A hell of a lot depends on how your mot tester interprets the guidelines, you rely on them for the service so it pays to get friendly.
Front fog lights are not a testable item. Plate lights should come on with side lights. Indicators must flash orange.
Dash warning lights must be seen to come on and go out again when you first turn the ignition on, if you remove the bulb it won't pass.
Removing airbags is dangerous, it's not a good idea to muck about with them and if you do then follow the manufacturers instructions to the letter. If the airbag light is on or flashing it's a MOT failure.
DT brakes are perfectly adequate if properly maintained, if they're not providing enough braking force it'll be down to an issue with old brake fluid, air in the lines, sticking pistons and/or sliders, or cheap/contaminated pads. With the drum brakes you would be better off cleaning them out completely and servicing the mechanism, else they'll seize up again in fairly short order.
Make sure your washer jets actually put a decent amount of fluid onto the swept area of the windscreen, no good having fluid if all your washers point at the pavement lol.
There aren't two horns, one is the siren for the alarm system and completely separate. If your horn doesn't work, get a friend to hold the button while you give the horn a few slaps, often this can dislodge any dirt blocking them and solve the issue. Try giving the plug a wiggle if this doesn't work, a lot of electrical problems tend to be fairly basic issues such as corrosion causing a poor connection etc.
Seatbelts mustn't be frayed, must release under tension and must retract fully, mounting points must be secure. The seat backs should lock in the upright position and be securely affixed to the bases. Any rust within 6" of the seat bases or seatbelt mounting points will fail.
Wing mirrors should be secure, if it's taped/glued back on and doesn't take much to knock off they will most likely fail. You must have at least two working mirrors, one of which must be the os wing mirror.
A hell of a lot depends on how your mot tester interprets the guidelines, you rely on them for the service so it pays to get friendly.