Don't exchange money in or near airports.
If you must, do so only in small amounts that will get you somewhere else. These are places of last resort, and they charge accordingly.
Don't exchange large amounts before leaving home.
On arrival, better rates are usually waiting for you. It will be necessary in most cases to have enough money for a ride out of the airport. Most travelers find they can do this for the equivalent of about $100 USD. Exchanging much more than that at home is going to cost you in the long run.
Make smaller, but more frequent exchanges if the currency is faltering.
Avoid travelers checks in destination currency for those countries, since you'll be locked in to a higher price as the currency falls. Practice the reverse if your home currency is in sharp decline.
Don't exaggerate the importance of exchange rates.
It is unlikely you'll ever have to cancel a trip because of poor rates. At worst, you'll need to adjust your priorities and perhaps cut back on your expenditures a bit more than you'd thought necessary. Have a general idea of the rates, but unless they're changing radically, relax and enjoy your trip without checking them every day.
The key is to be aware of conditions and adjust--taking advantage when possible, or softening the blow with careful planning.
More information: Take a look at a some reader comment about currency exchanges.
