What's the big deal?
Right. You've forked out a large wad of your hard-earned cash for a great instrument. Do you just throw it in the corner of the room when you get home? Do you head off to gigs with a bin liner (or garbage bag for our American readers) wrapped around it? Nope... It needs a little more care than that. A few tips then to keep it in one piece and playing well.

Casing the joint
OK, so it sounds obvious but its important to protect your investment with a good hard case. That's all well and good if you've got a Strat or a Les Paul and can easily pick up a hard case to fit your guitar. As a custom guitar maker however, I know how it can be very difficult to get a case to fit some of the more exotic shaped guitars and basses out there. It is very important that your guitar fits snugly in your case. If it can move about, it can get damaged. I generally end up modifying an existing rectangular 'generic' case by adding some foam/polystyrene that has been cut to fit the guitar and covering it to match the lining as much as possible.
Rule number one: make sure its snug.

Your case has also got to be suitable for its purpose. If you're using it for storage and for travelling to gigs in your car on a Friday night, a standard moulded plastic or plywood case is fine. If however, you're planning a nationwide tour and your case will be travelling in the back of a van full of amps, monitors, drum kits, etc. you need something that will offer you a little more protection. You should strongly consider a proper flight case - metal, reinforced sides and corners - the whole hog. This recommendation becomes pretty much an essential if you're planning to travel by air with your guitar (more below).
Rule number two: make sure the case is up to the job.

Environmental protection agency
Extremes of temperature and humidity are not the friend of the guitar. Something to be aware of when storing or travelling with your guitar. Although even more important when dealing with acoustic instruments, this is not something to ignore for your electric.

The best advice is that you need to avoid rapid changes from one extreme to another. For example, you've put your guitar in its case at home and travelled to the venue you're playing in that night. The environment in the gig venue is likely quite different to that of your home. Don't shock your guitar by whipping it out straight away - give it twenty minutes before opening the case to acclimatise more gently. As luck would have it, this is just enough time to get yourself a light ale before commencing your setup.

Other things to avoid include leaving your guitar next to a radiator or in a spot where it receives direct sunlight; storing your guitar in a car or van; storing it near doors or windows that could cause rapid temperature or humidity changes when opened; etc.

As you can see, its pretty much common sense. As a simple rule of thumb for storage or standing, if you are comfortable, your guitar will be comfortable.

Riding in my car
We've all done it. Popped our guitar in its case and stuck it on the back seat of the car for transport. I mean, what could go wrong? Well the first thing to remember is that your case is most likely black. Black cases just love soaking up sunlight and heat. Now think of a nice sunny, warm spot... Yep. The back seat of a car. Really, we're not just being paranoid here - the case and contents can get very hot, very quickly and guitars aren't really keen on extremes of temperature.

The other thing to remember about throwing your case on the back seat of your car is that its pretty much the same as placing a flashing, pink neon sign in your window that reads, "Thieves - Great Opportunity Here!". If you can't place your case somewhere out of the sun in your trunk/boot, at least throw a white sheet over it. It will keep the worst of the heat at bay and while it won't completely deter the thieving scumbags, it will at least cut the power to that neon sign.

Last point about car travel is to remember not to leave your guitar in the car/van overnight - especially in winter. Extreme drops in temperature are also frowned upon by your instrument.

Learning to fly
Flying with your guitar... Getting into scary territory now. I'm sure that many of us have looked out the plane window as the baggage handlers load the luggage. I'm sure that we've also been amazed at the punishment that they dole out to this luggage (apologies to any baggage handlers reading but hey, you guys are tough on those cases). Imagine your prized guitar sitting on the same trolley and getting flung onto a conveyor to drop unceremoniously on the floor of the hold. You'll probably appreciate the need for a strong flight case at this point.

There are some things that you can do to help matters though (and these are especially important if you're going to risk flying without a flight case). If money is no object you can buy your guitar its own seat where it can travel in comfort with you (you might even be able to get its intended meal for yourself). For those of us that are not in the extravagant millionaire category however, it is often worth arriving a little early to the airport and trying to charm the check-in staff into letting you carry your guitar on with you. If the flight is not full sometimes you may be able to talk them into it. Many times however, its not going to happen.

If your guitar has to go in the hold, ask check in if you can have the contents manually checked by them or by customs. This will provide some proof that your guitar was in one piece before the flight should you need to claim against the airline for any damage. After the guitar has been checked, de-tune it by about a tone and close the case in front of the staff. If possible, seal around the lid with tape and ask the staff to label it as checked. Then politely request that the case be loaded by hand and, if a separate hold is available for delicate items, request that it travel there.

On arrival, wait the prerequisite twenty minutes and open the case. Its better to do this in the airport if you can afford the time as its easier to make a valid claim before adding further travel and therefore further possibility of damage into the legal equation.