My sight reading has gotten very good, mostly because I worked at it. If it is monophonic or has common harmonies I can typically sight read close to speed after "reading" through without a banjo in hand.
This is in A notation. I have not taken the time to learn to read in the "Briggs" G notation. I also read in C or English notation for Classic banjo and have gotten to where I can sight read some pretty elaborate syncopation.
It you are reading tab-- throw it away and go cold turkey. Learn to read notation and study note duration. Approach each measure as a fractional math problem that must add up to divisions of the beat or time. Buy a good metronome and play to the clicks. I use a windup style with bell. I set the bell to match the signature of the piece with the bell ringing on the first beat. Electronic metronomes are great and there are even free phone apps that work. I like the windup though. If you buy a used one you will need to have it serviced by a watch/clock repair service. Chances are it will not keep good time.
Use a metronome with notation and 6/8 will be a breeze as it will all add up.
Notation is easy to read. Trust me, if I can learn it, anyone can learn it.
For A notation I like this book.
It is filled with interesting and easy pieces for sight reading and the musical instruction is clear and easy to understand.
If you want to learn guitar style or "Classic" banjo I recommend the A. J. Weidt studies. It was published in A notation as well as C. The A notation can be found on the Classic Banjo Ning site. It is an excellent work even for someone starting from scratch.
I am a pianist, and sight reading has never really been the issue. The challenge is reading between the lines. Which string/position is a better choice? Are the notes really as written, or are they an approximation? Some songs I am still working on, trying to improve. I've changed my fingering. Working with a metronome I've learned how to play more cleanly. How do you take ownership of the song? What tempo works for you? Where are the accents? Injun Rubber Overcoat is a good example. As Greg Adams said, "swing it." It takes on a different character.
For tunes i particularly like, I tend to want to play them on more than one type of instrument (banjo, penny whistle, epinette, mtn.dulcimer, and yes bones too I consider an 'instrument'). So I generally approach a new tune by trying to hear its plain melody line in my head. Even tunes written in tutors for banjo have a root melody line that can be partially hidden among the 'banjoistic' fingerings and flourishes. Such flourishes or 'settings' will be added unique to any instrument- fiddle ornaments and fingering moves are typical to fiddle and whistle ornaments are specific to whistles, etc.
For me it really helps to try and hear the plain melody in my head... at least for the first time or two in hearing it... before plunging in to learn the instrument-specific 'licks' and ornaments. It helps me get my bearings and understand the tune's structure better.
Unless a tune is merely a bunch of fingering patterns, strums, and flourishes strung together (and some do seem to be not much more than that), under them are usually the bones of the tune, which can then be played on other instruments with different decoration or syncopation applied- to either stand alone as played on a different instrument or to blend pleasingly in a mix of instruments playing together.
Very true John. As the years of banjo went on and subsequent generations took it up they learned how to write notation better. By the late 1880s banjo notation specific edits became more or less standard. By the late 1890s they figured out even better at the edits.
All of these concerns can be solved by a knowledge of these edits and the use of a pencil.
Left hand fingerings, positions, barres, string indicators, and (for guitar style) right hand alternate fingerings make reading and playing seamless. Much of the "early" music does not need any of this as they can be pretty straight forward.
In addition, as the years and generations go by, people get better at playing banjos-- figuring our easy left hand patterns. This is reflected in the later compositions and can be retrofitted to the early stuff to make it much easier to play.