One of the most important aspects of your banjo set up is the head tension. Changes to your banjo head tension dramatically affect the tone of your banjo. It can also alter the playability of your banjo. Luckily, this is one of the easiest parts of banjo setup to take care of yourself.
A banjo head differs from an acoustic guitar top or other stringed instrument with a wooden top because the stiffness of it can be altered by tightening or loosening it. In stringed instruments that have wooden tops, the top wood used and the tension built into it via thickness, bracing, arch (on arched top instruments such as a violin) is extremely important and it is very hard to change (if possible at all) after the instrument has been built. Banjo heads have the benefit that this can easily be changed by adjusting the tension bolts or by entirely changing the head. There are a wide variety of head materials offered that allow for different tone ranges depending on the preferred banjo sound.
At Deering we adjust our head tension by tightening it to a pitch. We mute the strings and tap the head around and listen for the pitch that is made. The most important part of this is to have even tension all the way around the head. To make sure the head tension is even we want the pitch to be consistent all the way around.
How tight you want the head is determined by the tone you want to achieve out of it. A tighter head will give you a brighter tone and a less tight head will give you a darker, warmer tone. There is no set rule as to what is correct.
On most of our banjos at Deering we tighten the head to just above a G# pitch. This brings out the tone that the strong majority of banjoists prefer. It will give the banjo a bright, crisp, and clear tone, without being overly harsh sounding. Some traditional bluegrass banjoists like to go up to an A note. This gives the banjo a very bright tone. I would not recommend going any tighter than this though as you will start to move into territory that could cause the head could break.
Some modern 5 string banjoists such as Bela Fleck tune their banjo head down to about an F#. This gives the banjo a very warm tone and is good for modern styles of playing similar to what Bela, Noam Pikelny, or Ryan Cavanaugh do.
The head tension also affects the playability because a looser head will allow the bridge to sink into the head more, thus causing the string height (commonly referred to as "the action" of the strings) to be lower. Inversely, if you tighten the head, it will raise the action of the strings just a bit. Sometimes if you have a tiny buzz on your banjo, the first thing you should check is your banjo head tension.