Using an electronic tuning meter is the most accurate method in use today. I recommend buying or using the best meter you can find. All bands and recording studios rely on them or accuracy of tuning. Music stores will give you a lesson on how to use an electronic tuning meter if you ask them. Basically, you have to know what note you need for each string, (see chart above), turn the meter on, and turn the banjo tuning peg for that string until the meter indicates the string is in tune. Less expensive meters may only have a slide button to select the note you need and a light to indicate if the string is in tune. These are usually the older guitar tuning meters. Better quality meters have an needle indicator to show if the string is higher or lower in pitch. The best quality tuning meters will have a ‘hands off’ feature. This means you just turn the meter ‘on’, pick the string, and the meter indicates what note you have played. Some tuners have a needle, high and low lights, and a background light for use in dark areas. Turn the banjo tuning peg until the meter indicates the note you need and shows you are in tune. Continue until all 5 strings are in tune. Sometimes you have to do all of the strings several times if the banjo was really far out of tune. The performance of the electronic tuning meter varies with the battery strength. Make sure you turn the meter off when you are done with it.
Well, so much for tuning, gets lots of practice. If in doubt about your tuning, get a meter and use it until you are comfortable enough to argue back to someone who thinks you are out of tune. Prove it to them by showing it to them on the meter. Then check their instrument for tune.