If going by plane...
Don't get caught by the travel gustapos! Contact your airline far enough ahead to find out about their rules and regulations.
According to federal guidelines, all pets traveling by plane must be at least 8 weeks old and must also be weaned for at least 5 days. Also a health certificate that was completed within the last 10 days must accompany the pet. Make sure your vet is certified to complete such a form because not all vets are! You will also need a valid rabies vaccination certificate for the pet, and this certificate will need to travel with them.
Give thought to the weather as your pet will be briefly exposed to the weather outside during boarding. When temperatures are hot, it is best to fly in the early morning or the evening. If it is cold, traveling during the day is best. If you can swing it, try to get a nonstop flight and avoid plane changes.
You will need to make ample time for letting your pet stretch their legs out and take a potty break. Many airports now have designated areas to walk your pet. For example, at the Phoenix Sky Harbor International Airport there are 2 dog parks -- The Paw Pad and The Bone Yard. In these spots, there are water fountains for pets and "mutt mitts" for disposing any waste left behind. Don't panic if your pet chooses not to use the restroom; it all depends upon your pet's disposition and personality. The point is that you give them the opportunity if they need it. Call the airport you will be using to find out the specifics of what is available.
On another note, don't be surprised if your pet is not hungry while in transit. In fact, it is best that they travel on an empty stomach to avoid vomiting. No one likes to have to sit in their own accidents! If your pet is prone to nausea, please see our page on Motion Sickness.