I am thinking about what I need to do for maintenance whilst on a long distance tour I am planning. can anyone help me out with this?
This will depend on what kind of conditions you're riding in, what condition your bike is in, etc, but I think these are the basics:
Naturally other things can go wrong, but I think these are the main things that you can rely on going wrong or needing attention.
And don't forget maintenance on your body. Be prepared for sunburn, saddle sores, hotspots on your feet, muscle aches, etc.
I'm surprised no one has mentioned brake blocks. In my experience these wear faster than tyres or chain. I get maybe 800-1000 miles from a set of brake blocks.
I've now switched to the v-brake "insert" kind, which are marginally cheaper and much quicker to replace.
Always carry replacements and keep an eye on wear. When they are nearly worn down, carry two full sets (front and back).
If you're talking about regular maintenance (instead of fixing stuff), then I'd say the most important thing to do is to clean the chain, and lube it after cleaning. The chain is by far the part of the bike with fastest turnover, and the right maintenance can more than double the lifespan of the chain and, most important, of the whole drivetrain. This is specially important if you ride off-road, but also if you ride wet weather where road grime is thrown on the drivetrain by the wheels.
Second to that, it is important to have your bike prepared PRIOR to the trip, and that means mostly wheels: properly installed tubes and tires, with protective strip inside the rim, well tensioned spokes, and hubs. Hubs should be preferrably waterproof (rubber washings), with clean grease and right adjustment (not too tight, and with no significant lateral play).
Attachment of luggage/racks can become a great problem if you don't ride the smoothest of pavements, and it might be a good idea to carry some bungee-cords to make eventually shaky panniers more firm (wrapping them around the bike), and using thread-locking products (loc-tite) in the pannier bolts can spare you a lot of trouble (I have lost countless bolts due to vibration).
I'm not sure being over-cautious with air pressure does more good than harm. Messing too much with pumping and inflation can stress the valve system, and usually even not-ideal tubes can be ridden fine being inflated only once a week. Usually, you can just lift and drop the bike over its tires, from one inch or two high, and the bounciness will give you a hint if the tire pressure "feels right". Sitting over it and bouncing yourself on the saddle and on the bars will make an underinflated tire immediately show off, and it is a very natural and function-related way of checking tire pressure, after you get used to what "the right pressure" is supposed to be, and how it looks and feels.
Depending on weather, another issue is brake cables and conduites. If you get too much dust and/or rain and mud, the braking power can be much reduced due to inner friction in the cabling system of the brakes, with levers becoming hard to activate. While cleaning helps, replacing everything is guaranteed to give back the best braking performance.
From personal experience, I think that's it, hope this helps!
Mainly air the tires daily and fix flats. You should also give the bike a once-over about once a day checking for loose bolts & fittings, etc. In particular, check for loose cranks, as a loose crank can muck things up really quickly. Check the pressure in your tires (squeeze them with your hand) every few hours.
You should have the bike serviced before you start, so that the headset and wheel bearings are properly adjusted -- they should not need adjustment on the ride, though it doesn't hurt to check them from time to time for looseness.
The chain might need cleaning, depending on conditions and how far you ride. Generally for a 1-week, 500 mile ride the chain should be fine. Longer distances or exceptionally dusty/muddy conditions may require cleaning, and the chain should generally be replaced after about 2000 miles.
If there is a mechanic supporting the ride you don't need much in the way of tools. Otherwise, you should have some basic tools and spare spokes and repair links for the chain (plus tools to deal with both). And some spare bolts, etc. I've had rack bolts go walkabout, eg. Some tape (electrical, medical "adhesive", or, my favorite, hockey tape) is good to have, along with some "zip ties", for making emergency repairs. (I recall one rider who did about 20 miles with a tire repaired with adhesive tape.)