A nicely maintained bike is safer and nicer to ride,  the main thing for spanner phobes is to make sure the engine has enuf clean oil, the rest is not so dear to repair.  not changing your sparkplugs makes for hard starting, but doesn't damage engine.

 

One of the best ways to wear your bike out is leave it idling cold,  the so called 'warming it up'  
during cold running,  incomplete combustion results in 'combustion acids'  that etch the bore and cause it to wear out and blow smoke, 

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the best way to warm an engine is under a light load,  which means low gear,  medium revs, 
some people think that low revs is a light load,  but that's hard on the engine,  like starting your 10 speed bike in top gear, 

engines like to rev,   if you are at low revs in a high gear,  that also puts a lot of pressure on your head gasket,  which hasn't got much tension on it when the bike is cold,    I think aprilia advises owners to idle for a bit before starting off on their big twins,    but for most part,   put your gear on,  start the bike,  rev it a few times with clutch in, to unstick plates for a clean first gear selection,   then drive off gently,  increasing the load as it warms up.

 

with regard to Jap bikes only, 

manufacturers often recommend  10W-40,  I use 15W-50,  australia's a hot country and as bikes wear, they get on better with thicker oil,  I use semisynthetic,  bulk car oil,  which costs me around $5/liter,   there is no longer any additives in oil that damages clutches,  they all use the same ad pacs,  additive packages,  SH and SJ aren't suitable for bikes,  I think my semisyn is SL,

 

in the nineties,  the best oil you could get  was SG,  which is what a lot of bikes built then were designed for,  but semisyn is better, 

Unless you're racing,  don't worry about using full synthetic,  it gets contaminated with blowby (combustion gases going past piston) just like cheaper oil does,  and some of the really thin stuff gives harsh gear changes.

Oil is checked with bike upright,  dip dipstick, don't screw it in,  a few mm above or below the marks or window won't hurt it,  but if the oil level is too high,  it can blow gaskets and seals,  get pushed into the airbox,  fouling filter and then plugs,

also,  high oil level can mean the carbs have dribbled fuel into the motor diluting the oil, which will damage the crank,  check if the oil is thin and smells of fuel, if so,  this needs urgent attention, 

 

Use single hex sockets to work on motorbikes,  double hex ones damage small bolts,  and are good for fishing weights,  make sure you turn the sump plug the right way,  it confuses lots of people by being upside down, if you're really dyslexic,  set your ratchet to undo before you get under bike.

If you can't get at a screw on oil filter to undo it,  you can hammer a philips screwdriver right thru it sideways and loosen it with that.

no doubt you're not sure how tight to tighten sump plug,  suzuki ones have a fine thread and can strip easily, 
'specially if you car mechanic mate helps you,  

basically,  to tighten any fastener,  do it up a bit,  then test undo it, does it provide some resistance?  if not do it up some more, 

it won't become as tight as when it's been sitting for a while,  but you can get an idea of how tight it is at least,   or buy a torque wrench of course.

New spark plugs have a 'crush washer' and feel like they're stripping when you tighten them,  but keep tightening until you get a solid resistance to undoing, hopefully the last spanner jockey hasn't already damaged the thread.

don't put cold plugs into a hot engine, they go too far in, and when the same temperature,  lock together, and they break or strip threads when trying to undo, 

 

I change airfilter according to dustiness of riding conditions,   if it looks dirty it is dirty,   some of them filter from the inside, so make sure you're inspecting the correct side of them. I often change from paper to a square of oiled filter foam if they're expensive.

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Check if coolant is clean, and full in radiator,   a worn radiator cap lets coolant out when engine is hot, but doesn't suck it back up when it's cool,  premix coolant can be 30%,  bikes really need 35 or 40%, made up with distilled water from the ironing section of your supermarket.  Coolant is an alcohol,   and goes sour from heat and exposure to air,  like wine turing to vinegar,  so it needs replacing periodically.

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Oil clutch cables with chain oil,  not chain spray which will glue them up,  and throttle cables with sewing or airtool oil, or light fork oil,  2 1/2 or 5 wt,     WD 40 / CRC is for undoing or washing parts,  not lubing them.

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Brake and clutch lever pivots should be taken apart and greased wi moly grease,  you can just drip a bit of chain oil on top of the footbrake and gear linkages,  some of it will find it's way in.

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Those overly plentiful kawi GPX's and ZZR's require occasional rear shock linkage dissassembly, and greasing,  otherwise they wear egg shaped, and can flutter or patter over bumps, greatly reducing traction.

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Chain manufacturers still prefer you use oil to aerosol,  chain oil is cheap if bought as chainsaw bar oil,  I pay about $20 for 4 liters, but if it's raining a lot,  aerosol will stick better.  You are oiling the O ring part of the chain, from the inside,   as in,  lube the chain under the swingarm,  not from the back of the sprocket,   whatever falls in the middle will take care of that interface.

 

Clutch and brake levers should be adjusted to a height that gives a straight line from your shoulder to top of handgrip,  to top of lever,  line your fingers flat on top of bar to check,

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Gear lever should be adjusted sufficiently angled down to give clean upchanges,  particularly between 1 and 2nd, which has to go thru neutral,  and if you don't select 2nd in a firm positive fashion,  it could jump out of gear,  bending the shift fork slightly,  until it won't stay in gear properly, and you need to throw 1500ish to fix your gearbox,

when you go from a 250 to a 1000,   30HP to 180HP,  the gears are like 4 times as large, 

make sure you push the gear lever hard enuf to properly sink that next gear in.

 

Be very careful not to overtighten chain,  usually 25 to 40 mm up and down in the middle,  30 to 40 is prob safer,  and make sure it hasn't got tight and loose spots, by checking the tension for a full lap of the chain,  make sure it runs smoothly afterwards,  when you tighten the back axle after adjusting,  the chain often gets a bit tighter for some reason,  if that has happened, and you've got less than 25 mm, top to bottom of chain slack movement,   or it feels a bit rough as you spin the wheel,     loosen the axle again,  and slacken the chain a bit more, 

If you take care to adjust both sides perfectly evenly,  next time you want to adjust chain, you can mark the adjuster bolts wi a texta, and just move both of them half or one turn,  saves heaps of time.

 

To change brake fluid,  you can undo the reservoir cap, then undo the the calipers,  push the brake pistons all the way in, to push the fluid to the top,  mop out the top reservoir with a tissue,  fill it with fresh fluid,  block the pads apart with a spacer, and pump it down,  undo a bleed,  put your finger over it,  and pump it past your finger until it changes to clean,  then tighten it and do the other side,  then remount calipers and pump the pads against the disc, keeping an eye on the level in the top reservoir.

This is much quicker than draining lines and refilling,  and playing around to get every bit of air out,
before I start, I always bleed a bit off the top banjo bolt, to make sure there's no accumulated air at the top of the lines.

Some books say to do every year,  I'd do it if it looked a bit dirty,  maybe five years,  more often if you ride a lot in the rain.

 

I usually wait until I'm doing fork seals to change fork oil,  but I haven't got much time on my hands,  for years Honda recomended using ATF,  automatic transmission oil in forks,  lots of road bikes use 10 weight, which ATF is,  and it's cheap,  and certainly is designed for a hard life.   Oil weight changes damping,  so you can use or  blend a different weight to retune your damping.  or add some spacers to the top of your older forks if you think you've got too much sag.   Ideally suspension rises quickly but without a tendency to bounce.

Check any parts you've played with a couple of days later to make sure they aren't coming loose.