If the tape well in general looks dusty or grungy try to clean it up as best you can. A can of compressed air can be very effective. The alcohol usually evaporates quickly, but it doesn't hurt to go over everything with a dry swab to make sure everything is dry. Many decks have removable doors that make them easier to clean. Clean the heads about every 20-50 hours of use.
Some decks get dirtier faster than others.
If there is more than just a hint of brown stuff on your swab, you need to clean your heads more often. It does not hurt to do it too often. Demagnetizing There is much controversy concerning demagnetizing. A few say it needs to be done often, some say only once every few years and many say not at all or only when necessary. One thing I will say is DO NOT use the cheap demagnetizes that you find in record stores.