Fleas can transmit disease and tapeworm. Keeping your pet and his environment clean is the single most important part of a successful flea-control program.
    Steps: 1.  Understand the life of the flea. An adult female can lay one egg per hour for every hour of her life (usually three months). Fleas thrive in heat and humidity and are most active in summer and fall.   2.  Help prevent fleas indoors by vacuuming your home thoroughly and frequently, paying close attention to corners, cracks and crevices. Dispose of vacuum cleaner bags conscientiously, as adult fleas can escape.   3.  Remove fleas from your pet using a fine-toothed comb, and drop the fleas into soapy water to drown them.   4.  Wash pet bedding in hot, soapy water weekly; this is the most likely site for flea eggs and larvae.   5.  Prune foliage and keep grass trimmed short to increase sunlight, as flea larvae cannot survive in hot, dry areas. Remove piles of debris in areas close to your home.   6.  Bathe pets weekly if possible. If bathing is not an option, speak to your veterinarian about appropriate alternatives.   7.  Watch your pet for signs of flea trouble: excessive scratching and biting, especially around the tail and lower back; 'flea debris' (black, granular dried blood) and fleas themselves on the skin; and possibly raw patches where the animal has been biting and scratching himself.   8.  Talk to your veterinarian about various treatments for your flea-plagued pet: a flea adulticide applied monthly to the skin; a monthly pill that prevents fleas from reproducing but doesn't kill adult fleas; and multipurpose products that prevent flea reproduction and control heartworms, hookworms, whipworms and roundworms. Also consider flea collars and flea powders.   9.  Look into chemical flea-treatment products to apply by hand around the environment in spray or powder form. Ask your veterinarian for a recommendation on the best product and how to use it.     Tips: Be diligent in your exterminating efforts. A flea pupa while in the cocoon is impervious to treatment and can live for eight months without feeding.   Veterinarians are skeptical of homemade flea remedies such as garlic, vinegar, vitamin C and kelp.   Call on a professional exterminator for severe indoor and outdoor infestations.     Warnings: Be very careful with all insecticides to be used on pets or around your home. Read directions carefully.   Never apply a flea product to a cat or kitten unless it is labeled as safe for cats. Cats are very sensitive to insecticides.   Ingesting fleas could give your pet tapeworm (see related eHows about preventing worms).   Tips from eHow Users: Flea eradicator for cats
Every time my husband and I visit my in-laws we leave our cats with my parents. Every time we go back home our cats have gotten fleas from my parents cats. Here is how I eradicate them, without poison and very cheaply. (it usually takes about a month, sometimes longer depending on how diligent I am)

First, my cats are indoor only. So they are not constantly tracking in more fleas. I close all doors to rooms the cats do not need to be in (our bedrooms and the computer room). This makes the contaminated area smaller and easier to deal with (plus I don't have to worry about being attacked at night by hungry fleas).

I bathe the cats using the all natural shampoo I use on myself. Fleas can swim, but not very well and any kind of soap will cause the adults to drown. The eggs on my cats are also rinsed down the drain (and yes, fleas lay the eggs on your pet, they are not sticky though and fall off easily, you can see them if you brush your pet on a dark surface like black construction paper, the eggs are very small and white). I use something natural (be careful of certain natural oils and things that can be poisonous to your cat) because whatever goes on the cat will go IN the cat as soon as they lick themselves. Some adults will survive. That's OK. I continue to bathe them every week until a few weeks after the fleas are gone.

I use an all natural herbal flea collar, it smells great and doesn't poison my house or my cat. (the pennyroyal tip is a cheap way to make one if you have a garden and like to sew, but if you are like me natural foods stores will usually carry some commercial versions that look like regular flea collars but smell better)

Vacuum every day. Throw out the bag or keep the vacuum outside. The vibration of the vacuum causes the pupa to hatch so you can kill them.

Take an old towel (or towels, or blankets, whatever) and put them where your cat sleeps most often (for us it was the back of the couch, and the chair in front of the window). Throw this towel in the dryer every day. Any fleas living in/on it will be killed. Wash it at least once a week. This is also a good way to protect your furniture when you don't have fleas. Also wash any other cloth they may be near at least once a week (like the throw blanket on the couch).

If you have a really big problem (or if you just want to anyway), shampoo the carpets. The heat and soapy water kills them as well as deep cleaning so that even the ones way down there get sucked out. Again make sure to use carpet shampoo that is safe for your pets.

Most importantly: take regular table salt and spread it all over your carpets. Wait at least 30 minutes and vacuum. Some people will vacuum, then salt and leave the salt on over night. The theory is that the flea larva (like the caterpillars of fleas) will eat the salt and die of dehydration. This really works. I have done only this part when I was really busy and it took longer but it got rid of all the fleas.

Safety: I am pregnant right now (and just got my cats back after a long vacation). I can not be around any poison. Salt=safe, shampoo=safe. I can't use pennyroyal because of my pregnancy.

Costs: Salt=Cheap (you probably have it sitting in your kitchen right now, if not buying some is cheaper then the gas you will use to get to the store) Shampoo=cheap (again, something you probably already have, just make sure the kind your have is safe for your pet).