I've done quite a few miles, in the air and on the ground - here are a few tips I've learnt.
Travel light - every time I return from a trip, I swear that I'll carry less next time! If possible travel with just hand luggage - it can be done, and then you're first out of the airport.
Always use a Lonely Planet.
Never be the first into a customs hall, if possible always let some one else in first!
Always be nice to the check-in staff, even if the plane is late or delayed.
Dress well, and ask for an upgrade!
I know it's obvious but if you can afford it travel Business class on long haul flights, or at the least premium economy.
Carry a mini MP3 player. Don't fill it with all music tracks, download some "spoken word" stuff, there are loads of radio plays etc you can get (my favourite is Sherlock Holmes) they take up less space than music as the quality doesn't have to be that high.
For a long flight try to get a pair of noise canceling earphones - they do cut the engine noise a bit!
Don't use a backpack when you are out and about - get a local plastic bag - you won't stand out so much.
Find a bag you're comfortable with - I've got a backpack which you can zip the harness up and convert it into a bit of soft luggage - handy when going through customs or checking into a posh hotel!
Always join the frequent flyer club - you never know when you'll fly again, and most clubs are now linked with other airlines (also most allow you to earn miles from other activities hiring a car, or booking a hotel).
Work out what perks the frequent flyer club offers - you might be able to check in at Business Class check-in desk, get into the lounge, or get an upgrade to Premium Economy.
Make sure your passport has at least 6 months before it expires, most countries state this as an entry requirement.
If you're an EU citizen, and you're travelling in the EU then make sure you have a "European Health Insurance Card" (this is the replacement to the old E111 card). You can get an application form from the Post Office.
Make sure you have all the jabs required for your destination. Talk to your doctor to work out if you need any, or if you're in the UK ring NHSDirect.
If necessary, get your visa(s) before you take off.
Bring a good book with you - travel related? "Around the World in Eighty Days", "Travels with my Aunt", "The Art of Travel" or "On The Road".
Be wary of starting conversations on a long distance bus trip. Your new "friend" may have some views that alienate the rest of the bus, and you're stuck with them for four hours! (at least on a train you can run away to the buffet car!)
Worried about too many items of carry-on luggage? Get an airport duty free bag, and put as much stuff as you can in that!
Book your holidays around the Easter Bank Holidays - that way you get two extra days for free. If Easter is late, you might even be able to include May Day as well!
Always travel with travel insurance, and always bring the insurance details with you! I'd say the most important item is the Health insurance - a million pounds cover is the minimum I'd accept, and the more the better, especially if you are travelling to the USA.
Spread the load. Travel with some cash, some Travellers Cheques, and some credit cards (one Visa and one Mastercard if you can arrange it!)
If you're sent abroad on Business, see if you can extend your trip by a few days, and see where you can get to. I turned a trip to The Netherlands into a long weekend in Spain, by getting the overnight train between Paris and Madrid!
Always bring a small sponge with you, washing is so much easier with one, and they weigh next to nothing.
I always bring one of those plastic 'change' bags that banks use to hold coins. When I leave the UK I put any UK coins that I have in my pockets in the bag - that way I never get foreign coins mixed up, and my UK change isn't rolling around in the bottom of my bag when I get back from my trip.
Buy some lightweight clothing, the chances are that it will be quick drying also. If that's the case, then you don't need to pack as much! The best purchase I've made is some silk boxer shorts - they weigh nothing, and dry in an instant.
If you are doing laundry in your hotel room, then use the "towel trick" to dry clothes faster - just roll your damp item of clothing in the hotel towel, and then wring the towel - you'll be amazed at how much drier the item becomes!
Don't bring a BIG tube of toothpaste with you, find a small tube, and if it's half used so much the better. You can also get "travel versions" of shampoo's and shower gels, that cuts down on the size and weight!
Tell your credit card company where you are going, that way they won't stop your card when they spot it's being used half way around the world.
Check the cost of using your credit or debit card abroad - getting cash out on a debit card is cheaper than a credit card. Also, not all card issuers charge the same for foreign purchases. In the UK Nationwide offers a Visa credit card that does not charge the Visa 2.75% foreign currency charge.
Check when you have you have to pay your credit card bill by each month, if it's while your away make sure you set up a Direct Debit for the minimum amount or the credit card company will charge you for non payment.
Before you go take a photocopy of any city maps in your guide book, that way when you're there you can bring the photocopy of the map out with you, and leave the heavy guide book behind in your room. If your digital camera has a big LCD screen then take a photo of the map, and use that! The bad news is that if you keep getting lost, you might flatten your camera's battery!
If you have a choice of which queue to join at immigration, look at who is in the queue.. Chinese and Indians queue more tightly together than Europeans (I guess it's something to do with personal space). So a short looking queue can have a lot more people in it!
Take some passport photos with you - you might need them for visa's etc.
If you're passing through a city, and you don't have a hotel, but you do have luggage, head for the train station and see if there any lockers that you can dump your stuff in.
Unless you've got a great memory always keep a diary when you're travelling, even if it just states where you were on a given day.
Always bring a pair of earplugs with you!
Always check your boarding pass has your name on it before you leave check-in.