I can relate to what Wayne and Jen said earlier.
I used to wash Juni (and all my other cats I had) from time to time with special herbal shampoo (anti-flea effect) and I had her wearing a special anti-flea collar. It helps. A tip - I used to buy dog collars, they were exactly the same, except, dog collars were twice long and when you have two kitties, you cut it in two parts and staple the part without buckle
Of course, cleaning the place thoroughly is extremely important.