As many pet owners know, fireworks and thunder storms can cause a great deal of stress for some animals. Commonly seen signs include:
Shaking, trembling
Excessive drooling
Barking, howling
Trying to hide or get into / out of the house, fence, or other enclosure
Refusing to eat food
Some animals may lose bladder or bowel control or experience temporary diarrhoea from prolonged stress
Please note: The signs mentioned above are general signs, and could be indicative of many different diseases or conditions. Please consult with your veterinarian if these signs persist after fireworks or thunder has subsided, or if you suspect that your pet may have been poisoned or is otherwise ill.

Practice Safety

Keep pets indoors. It is advisable to close the curtains and turn on the TV or radio to provide some distraction. Calming or classical music are better than some TV or radio noise choices. Therapeutic music such as Through A Dog's Ear often work better at keeping your dog calm and providing an audio distraction.
Many times pets will seek out a small den-like place (such as a crate), if they are fearful or stressed. If you do not already have a crate, bed or similar place that your pet can call his "own", it is recommended to create that safe place and familiarize your pet with it as a means of reducing stress during fireworks and thunderstorms.

Use a leash or carrier. If you must be outside with your pet, keep the pet on a leash or in carrier at all times.
Practice fire safety. Keep pet away from matches, open fires, and fireworks - especially ones that are lighted on the ground. Pets may try to sniff (or eat) fireworks and pet hair can easily catch fire if too close to the fireworks.
Take pet for a walk first. If possible, make sure that you pet has time to "use the restroom" before the fireworks start. Some pets are too frightened to void once the fireworks begin, and this may lead to an "accident" later on.
Make sure pet ID is current. Make sure that your pet has proper identification tags, with current information, in case s/he gets away. This will help the local authorities (who are quite busy this time of year handling frightened runaways).

What can I do if my pet is frightened of fireworks and thunder?

Some animals do fine and don't seem to notice the fireworks. Some do well with just having their owner near, talking in a soothing voice and petting or holding the pet. And then there are some pets that cannot be calmed by petting or talking to them - they are simply too upset. Animals that are frightened/stressed can hurt themselves and possibly escape if left alone, and the results can be fatal. Frightened animals running loose are in great danger of being hit by a car.

For these animals, it is best to provide a safe place, such as a carrier, to be in while the fireworks last. This alone may be enough of a comfort to soothe some pets. If the carrier is not enough to calm the animal, medication (in the form of a tranquilizer) may be warranted. Tranquilizers are not for every pet. Talk to your vet about medical options that are suitable for your dog or cat. A patient-doctor relationship is needed before dispensing medications, so if your pet hasn't seen the vet yet, an appointment will need to be made to examine the animal to ensure that there aren't any underlying heart or other problems, and base any medications on current weight.

To help your pet become accustomed to thunder and other loud noises, you can try some behaviour modification. This technique involves playing a recording of thunder at very low levels. Use the time to reassure your pet that everything is fine. Gradually increase the volume slowly over time, as your pet is able to handle the sounds without getting stressed. Many stores carry "relaxation" types of music, and I have seen several rain/thunderstorm CDs available. This technique does require time and patience for it to be effective. Start slow, and do short sessions only at first. Praising the pet for remaining calm is important. Be careful not to overdo praising, you want the pet to feel that this is "situation normal" as much as possible.

Attention Seeking

Do check that the dog doesn't have a 'valid reason' for seeking your attention, like an upset tummy, which means he wants to poo outside! Your dog may also have a 'right' to be bored and want some fun, for example if he has been good and quiet for several hours while you have been ignoring him. You need to strike a balance between spoiling the dog, and making him brattish, and having a fretful, bored dog with too little to do.

You have more chance of controlling attention seeking if you only reward a dog for doing something you want him to, rather than just for coming up and nuzzling you. It's better not to pay immediate attention to a dog that is seeking it out of boredom - ask him to be quiet, and then pay attention to him for being good - but it's even better to ensure that the dog doesn't get bored in the first place. Old dogs like to snooze a lot, but young dogs need to run around off the lead, a lot, and benefit from a lot of interaction with their owners.

Structuring your dog's day is a good way to avoid attention-seeking. Dogs that seek attention in annoying ways are often predictable. They may have a manic period in the evening when you are tired. Try working out when the dog does this, an initiating an activity beforehand. Dogs tend to sleep after exercise, and if he hasn't been out much, give him something energetic to do. This doesn't have to be a long walk, if you are too tired, you can stand still and make him run! Try a ball game in the garden, or even indoors. Make him 'earn' the throws by sitting first, and even sitting and staying, only fetching on command, so he doesn't get too demanding. You can also play 'hunt the titbit' as a fun game indoors. Get him to stay outside the room while you hide the titbits, which he has to sniff out. Chews can also help keep dogs occupied when you are busy or tired.