Your vacuum cleaner is your best friend...
Vacuuming is one of the best ways to clear the air in your home and get rid of any excess pet hair that's made it into the floor or furniture. If you're prone to allergies of any kind - not just the feline variety - it's worth spending top dollar on a great vacuum cleaner with top-notch suction and the ability to pick up even the finest of pet hairs.
...and so are anti-histamines
Known for their ability to relieve hay fever symptoms, anti-histamine tablets and syrups (i.e. loratadine, cetirizine, chlorphenamine) lessen allergic reactions to pet hair too. If for whatever reason you can't use anti-histamines, there are other options in the form of nasal sprays, eye drops and more - ask your local chemist for alternative options.
Some cats are more allergenic than others
Even people who have spent their whole lives with cats as pets might not realise they're allergic until they're around a specific cat. This is because every individual cat differs in the amount of allergens they produce (and, surprisingly, it isn't always based on their breed).
The best way to tell if you're allergic to a certain cat is to spend some time with it before adoption.
Good hygiene goes a long way
If you're allergic to cats, lessen the symptoms after coming into contact. Wash your hands after handling them, don't allow them to lick your face, don't allow your pets to sleep in the bed and be sure to wash all sheets, blankets and pillows regularly. Cuddly toys are culprits too. It can help if your house has hardwood floors as opposed to carpet, as they're far easier to clean when it comes to pet hair.
A great pet is worth the trouble (most of the time)
For some people, practising good hygiene and self-care will ease allergic symptoms enough to be able to happily live with a cat in the house. But it's also important to be aware of the big possibility that, if the symptoms are too severe, despite good practices in the home, your cat may need to be re-homed. After all, your pet needs to be comfortable and happy as much as you do.