This is probably one of the biggest problems that irk all of us. There is no dearth of literature on this subject and its worth a read online. If you have a big house and lots of $$ then you can get a QT and have your fish transferred whilst leaving the main tank fallow. It's a long process. You will have to leave your main tank fallow for 8 to 10 weeks to break the parasites cycle whilst treating the fish in the QT with the hypo salinity method. This is the best method. Many of us will never do this for reasons stated above. I would advise against meds for various reasons which you can read about online. The best thing is prevention but many of us will end up getting ich because we are always itching to put new stuff into the tank! So what to do?
1.Keep your tank clean with the usual water changes. If you think additional water changes need to be done because of the signs (smell, discoloration of water, algae blooms) then do it. It will help to ease stress on the fish.
2. Supplement the foods you feed the fish with garlic and vitamins. Do this everyday until you see improvement.
This is the method i have used and its a hassle free thing. 90 to 95% of your fish will recover.
**Don't buy your fish from dingy notorious LFSs. Pay a little extra and go the extra mile or two and buy fish which are healthy. If you are staying in the East then you have two options but both are quite a distance. Hint hint.