Guinea pigs are easy to take care of, which is why they are such great pets.  However you should have some knowledge about their care to ensure a long, happy life for your cavy.

Before you bring your friend home, you should have ready the basics.  Namely a cage, food, and water.  The minimun size for a cage should be about 30 by 15 by 15in.  Make sure the cage does not have a wire floor, as a guinea pig's legs can easily be caught and broken in them.  Also, don't use a cage with glass sides as guinea pigs require ventilation.  The floor of the cage should be covered in bedding, but NOT cedar or pine bedding.  Cedar and pine bedding oils have been linked to liver disease in small animals like rabbits and guinea pigs.  I also do not recommend hay or straw used as bedding.  It is not very absorbant and can injure your pet's eyes if a sharp piece catches them(which I found out the hard way).  Give you cavy a place to hide and sleep in, such as a wood or cardboard box.

I have heard of many guinea pigs being kept in weather-proof hutches outside year-round, but I prefer to keep the cage inside during the colder months (when the temperature drops below about 60 degrees).  When the weather is warmer I place the cage on a porch out of direct sunlight.  If it gets above 80 degrees, a bottle filled with frozen water can cool the animal down for a few hours.  Don't keep your guinea pig outside in excessively hot temperatures; this can lead to heatstroke and death.

Cavies should be fed both guinea pig pellet food and fruits and vegetables.  Guinea pigs cannot make their own vitamin C, so it should be provided through water supplements.  Give your pet a bowl of pellet food a day in a small dish with a weighted bottom.  This will help keep your guinea pig from spilling the food all over when they stand on the edge of the dish.  Also provide your guinea pig with fresh vegetables like lettuce, carrots, and broccoli as well as treats from time to time like apples, oranges, and grapes(remove the pits).  I don't suggest giving them celery because the strings of the stalk can get caught in their throats.  Guinea pigs also need fresh water every day in a waterbottle.

Play with your guinea pig to give it excercise and brush it from time to time to remove shedded hair.  Every so often it is good to have your guinea pig's nails clipped.  It's best to watch someone experienced do this at first.  Cavy nails can be clipped with a small cat or bird nail clipper just outside the end of the blood vessel (can be seen as a pink mark in white nails).  If you accidently cut too close or on the blood vessel the nail will bleed.  Some baking soda usually will help stop the bleeding.

You can give your pig a bath in warm water and mild baby soap if it gets very dirty.  If you see your guinea pig scratching a lot it could possibly have mites.  Try giving it a bath.  If this doesn't help take it to the vet.  If your pig stops eating, take it to the vet.  If you notice it limping or acting very sluggish take it to the vet.  If it gains a lot of weight take it to the vet.  Basically if your guinea pig is acting unusually take it to the vet to make sure all is well.  If you are careful and loving, your guinea pig should live a long, happy life.