Check the bulbs all work at least once a week. That's the high and low beam on the headlight as well as the indicators. Don't forget to check that the brake lever and pedal both operate the brake light. Check the horn and the kill switch at the same time.
Check the tyre pressures are correct, ideally before every ride. If you ride every day then check them at least once a week. For the BMW F800ST the front tyre pressure is 36.3 lbs/in (2.5 bars) and the rear tyre pressure is 40.6 lbs/in (2.8 bars). The tyre pressures do not need to be increased when you are carrying a passenger or luggage. [The tyre pressure monitors have a centrifugal trip switch so they do not transmit a pressure reading (in bars) to the computer until the bike is travelling at more than 19 mph (30 kmph). The sensor readings are temperature compensated to 20 degrees C so they may not match with the readings provided by gauges at service stations which are generally not temperature compensated.]
Check the oil once a week. The oil level varies with the temperature so measure the level when the motor is at operating temperature. Place the bike on the centre stand on level ground, remove the dipstick and wipe it clean. Insert the dipstick until the edge is resting on the oil filler neck. The level should be between Min and Max. Take care not to force the dipstick in because it can get bent and damaged. Use mineral oils of API classification SF through to SH, engine oil 15W-40. Do not use additives because they can be detrimental to clutch operation. If you want to measure the oil level with a cold engine, start the engine and let it idle until the fan starts up, then let it idle for another minute, swiitch off and wait 1 - 2 minutes to let the oil return back to the sump.
Check the tread and sidewall for any cracks or objects wedged in the tyres. You need a minimum of 1mm of tread depth across a continuous three quarter's of the tyre's surface. If the rear tyre has squared off - i.e it has worn a flat patch round its crown - you may consider changing it even if it has more than the legal minimum of tread remaining. I am running on Michelin Pilot Power 2 tyres - dual compound tyres suitable for wet, cold road conditions.
Check the ground beneath the bike regularly for signs of an oil leak. If it's dropping black spots on the ground, carefully wipe the case with a piece of kitchen roll to fnd the source to find out where the problem may be.
Check the pads still have some life in them. You can do this visually. Put the bike on the centre stand and inspect the left and right brake pads looking from the front of the bike between the wheel and the fork tube. If the wear indicators, some grooves running across the edge of the pad as you look at it edge on, are not visible then have the brake pads replaced. The first set of pads were replaced at 13,600 miles.
You must display a valid tax disc. To get one your bike must have a valid MOT (if it's three years old) and you must have insurance. Insurance will be invalidated if either the tax or MoT runs out. The only journey you can make without an MoT is to a testing centre.
When I had the bike serviced in October 2009 I was having problems finding neutral. The service engineer said that the clutch cable was stretched. It may be worth checking and adjusting the clutch bite point occasionally.
Pedals mounted directly on the gearbox selector shafts are rarely a problem, but shafts that involve linkages are secured with small locknuts - it pays to check periodically that they are not coming loose.
When the engine is cold, carefully run your hand or a dry cloth along the base to ensure it's dry. Any wetness could indicate a leak.
Make sure the legs - the shiny parts - are smooth and free of pitting. If there are traces of oil on them, the fork seals may need checking.
The drive belt does not need regular lubrication or maintenance (unlike a chain). The quoted life is 25,000 kms but I had one replaced after 6,900 miles because of stone damage. When I had the bike serviced at 13,600 miles the mechanic said the second belt also had stone damage but I decided to take the risk of not replacing it.