Keeping your glass clean is crucial for the best tasting hit possible.
Whether its a bubbler, bong, or any glass piece, this is the best way to keep your glass polished for that smooth toke. Start by pouring Isopropanol Alcohol. (90% Can be found in the first aid isle of most major drugstores) The amount will depend on the size of your bong. If the glass is small(perks, bubbler etc.) you can pour the rubbing Alcohol in a ziplock. Half a cup is a good starting point but you will need to experiment. Then pour Epsom salt or table salt into the bowl and the mouthpiece. You can use a funnel if this makes it easier. Pour in however much is appropriate for the size of the bong. An average bong would need about 1/3-1/2 a cup. Now shake the glass for about 3-5 minutes. Multiple attempts will probable be needed depending how dirty it is. Simply rinse off with (preferably hot) water till its sparkles clean.
A clean, cold bong is so worth the limited effort it takes to keep it up. A good little secret that I want to share with you guys is the magic of lemon juice. The addition of lemon juice to your bong water keeps is smelling and tasting fresh longer. In addition the citric acid in the juice helps keep resin from collecting on your glass to fast.