Play on a single string. For beginners and novices, the easiest way to approach the song while building confidence and familiarity with the fretboard is to play it on a single string. Tablature available online (see Resources) identifies which string and which fret should be played. Here, in tablature form, are instructions for playing the opening melody in the key of G, beginning on the fifth fret of the fifth string (second widest).
A5|--5-5-5-0-2-2-0-9-9-7-7-5
Play on two strings. Beginning guitar players with a little more manual dexterity can choose to play the song on multiple strings. For example, switching to the the key of A, Old McDonald can be performed on the two highest-pitch strings of the instrument, this time starting on the open high E of the first string (no frets held). See Resources for the entire tablature in this key, but the opening melody tabbed out in Step 1 looks like this:
E1|---0--0--|--0-----|----------|--------|---4--4--|--2--2--|--0---|
B2|-----------|-----0--|--2--2--|--0-----|----------|--------|--------|
Play chords. A traditional performance of Old McDonald would not simply be a plunking of the individual notes in the melody. Instead, the guitar would be an accompaniment, playing chords while the lyrics are sung. The words of the opening line can be separated into measures like so: "Old Mc - Donald - had a - farm, - e i - e i - o." Each hyphen represents the start of a new measure and a chord change. Using the key of G again, the chord progression for the opening would be: D|D|G|A|D|A7|D
Improvise. The height of musical mastery is the ability to successfully improvise on an instrument. Thus, even on a simple tune such as Old McDonald, a guitar expert could add fills, walking basslines, solo sections, or even silence the guitar for a cappella verse, all to increase the enjoyment of the listeners.