If what you want to do is learn to play some tunes, then there’s no reason to stop and read what I have to say. Go and learn some chunzes! Â However, for those who are taking a break from learning tunes and want to start thinking about what it is they are trying to do and what it’s all about, the following stuff may be helpful.
To determine how best to play a particular type of tune I suggest that you find a good teacher and listen to strong representative players. At some point you’ll need to break the tune down into phrases to determine where to pulse it. Knowing something of the dance associated with the tune can help too. When disassociated from the dance tradition, a tune is called a “listening pieces” (i.e. a folk instrumental tune solely played for entertainment).  In order to develop your ear, you’ll need to listen for some main features of a tune.  In general, there are five things that make one kind of tune different from another kind of tune. They are your PALET.
- Pulse (placement of the emphasized notes)
- Amount of swing (more or less or none)
- Length of phrases (shorter or longer)
- Endings (groups of sixteenths, eighths, and quarters)
- Tempo (slower or faster)
These five features give you something to hold on to when you are trying to distinguish between types of tunes, especially when used with the descriptions that follow.
 
Up until  the advent of recording traditional tunes were passed down solely by ear, played in regionally developed styles, resulting in melodic and stylistic variation. The traditional musicians who recorded from the 1920s to 1950s represent a very small fraction of this stylistic variation, though it is still difficult to say whether the sense of authenticity that now pervades traditional music has always done so.  Field recordings of traditional players from the 1950s onward, when many more people became interested in capturing samples of the diminishing variation within traditional music, show some variation too, of course, but by then those doing the “collecting” had a strong interest in finding the unusual.  A massive amount of music went unrecorded.  So, at this point it is a speculative gesture to take a stance concerning the debates about innovation vs. tradition.
Today, when learning tunes some players will be very faithful to the way they heard the tunes, othrs will put their own mark on them  — sometimes unintentionally, sometimes not. We might, at first, expect that all tunes follow the same evolutionary patterns, but they don’t and probably never did. Ignoring dots on a page (i.e, notes on a staff), it is pretty clear that over the decades for which we have aural evidence some tunes have evolved considerably, others have changed just a smidgen, and some have not changed at all.  In some cases what started off as a variation becomes a separate tune. In other cases tunes that were once distinct become welded together over time.  The dots are an exception since they present us with the petrified bones of a tune, devoid of the life given to tunes by musicians.
At any rate, it is important to keep in mind that listening carefully to traditional players of different generations can provide a massive amount of information about tunes.  The key, of course, is listening. Relying on the dots while somewhat useful at first  is a hindrance as you progress. The dots are merely a guideline, they offer a mere idea of a tune, its dry bones. Don’t treat them as unquestionable and final, they are like a photograph of a person: useful for identification but not very helpful if you want to know what the person was like.  The living, breathing music is what you want to connect with. You will hear different versions and settings in different sessions. Keep listening for differences and pick them up to try them out.