There are many approaches to developing a song with the bodhrán. This is one.

A Note on Acquiring Songs

There are more and less traditional methods of searching for, finding, and selecting songs. A strict traditional approach involves receiving a song from a tradition bearer, while non-traditional methods tend to skip the person to person transmission. Regardless of your chosen approach, once you’ve found and selected your song, you’ll need to really learn it well so you can develop and pair a rhythm arrangement to the song without worrying about your execution of the singing.

Learn Your Song

Do memorize your song. To allow it to become a part of you and your experience, it’s best to lose any written assistance as soon as possible. Even better, ‘skip the dots’ (sheet music) and learn it directly from an audio or personal source.
If you can try to find out from whom your source learned the song, from whom they learned it, and further. Learn as much as you can about these people. This connects you directly to the historic human element and the life line of the song.
If you choose to put a contemporary spin on the song, check out versions from contemporary singers who are held in high esteem among other tradition holders. Ask around for suggested singers, versions, etc. You needn’t imitate them, but one should seek to find out how and in what manner they make their variations. It may not be as mechanical as one may think.

A Note On Vocal Range and Pitch

Many of us are not formally trained musicians. So, if this is your case, note that your voice will fall within a limited range of pitch, and your chosen singer may have a different pitch range than you. If this is the case, get a recording of the song, and learn it as best you can at the original pitch, then move the pitch choice down or up to a more comfortable key or range. Also, if you have access to musical instruments, transfer it to the piano (find someone who can play if you can’t) or learn it on a whistle in a key that fits the original source, then move to a whistle that fits your vocal range.

Now that you have your song . . .

Knowing your song inside and out is most important. Every song is a story, and the bodhrán should complement and support the song’s story development.

Bodhrán Rhythm Development

So, adding your drumming to a well seasoned song may start out simply as a strike on the one and three of a 4/4 time signature song, or keeping a simple jig rhythm rolling out for a song that asks for such a rhythm.
Ensure the drum rhythm and volume work with the rhythm of the tune and words, and try not to disrupt, muffle, or overpower the song delivery in any way.

To develop a more complex rhythm pattern, try interesting, though simple, variations to assist the tension in the story line of the song. As the story progresses, slight variations in the bodhrán work can assist and support the developing tension. Often times, no development in the drumming is necessary. If the song is powerful enough on its own (and most are), then the drum work needn’t be too complicated.
A more contemporary song? Alter the rhythm from a 4/4 to 3/4/ or 6/8 rhythm. Or use a different traditional song tune that fits the lyrical content.

Put the Song & Rhythm Together

Play your chosen drum phrase(s) enough to play it automatically and sing at the same time. This is where keeping it simple will help most. The benefit of starting your drum work out with simplicity is that you can quickly play the rhythm while singing. This will allow you to develop over a long period of time more complex and appropriate rhythm patterns. After playing and singing the tenth time, say, you may notice that a break in the pattern here, or an increase in pitch there, will support the melody line and narrative of the song. It’s less likely you’ll notice these aspects if you develop a complex rhythm pattern prior to putting it to the song. Let the arrangement live and grow for a time, and you’ll discover what works well and what doesn’t. Eventually, you may get to a point when you rarely play the rhythmic accompaniment exactly the same way every time. You may end up changing it up depending on the situation and mood of the room.

Rhythm Pattern Development Ideas

Try out new pitch ideas: move higher in pitch to increase the tension in the song. Be careful to ensure the pitch does not ‘clash’ with the songs melody lines. Drop low to provide a sense of sorrow or thunderous omen. And don’t forget that resting for a bar can really highlight a song lyric dramatically! Explore the possibilities, although refrain from overpowering the song in any way.
Work out a drum intro or an appropriate solo to follow the song.
Work out a turn or bridge or chorus rhythm to match and support the song chorus (if any).
Remember to record your experiments so you can reflect on and assess your work. This allows you to really understand how what you’re doing affects the emotion and feeling in the song.

So, start out easy and simple. Don’t overcomplicate anything. And have fun!