To do this in general, one must develop a feel for 4:3 (four against three). However, since this appears to be for a solo instrument, there can be a simpler option. Here are a few common techniques for handling this situation:
1. "Changing" the time signature (i.e., Count the beats differently)
On an instrument like piano, it is sometimes necessary to play a "true" 4:3. Say, the right hand is playing triplets against sixteenth notes in the left hand.
However, on a solo instrument, there is sometimes a "cheat" which would seem to apply here. Rather than counting the measure in four beats, count it in two (if you're comfortable with 3:2) or even one (especially if the tempo is fast). In the latter case, the half-note triplet just becomes a "normal" triplet.
To do this most effectively, start counting in 2 or 1 a few measures beforehand, so that you have the feel well established, particularly of the downbeat, before getting to the triplet.
2. Counting it mechanically (least common multiple)
Divide the measure into twelve equal pulses
- Divide each of the measure's four beats into three sub-pulses (i.e., triplets) — so, twelve total "pulses".
- Divide each of the triplet notes into four parts — again, a total of twelve pulses.
This will show how each triplet note aligns with the beat.
- Starting at a very slow speed, count to twelve, tapping one hand on the main beat and one hand on the triplet beat.
- As the rhythm becomes intuitive at a slow tempo, begin to speed up.
See graphic below.
Very similar to the above.
- Count triplets for each main beat, emphasizing the part of the beat where the half-note triplet occurs.
- Count the half-note triplet in four-pulse units (i.e., like counting sixteenth notes), emphasizing the main metrical beats.
MAIN EMPHASIS / _secondary emphasis_ (or vice versa) ONE two three _one_ TWO three _one_ two THREE _one_ two three ONE two three FOUR _one_ two THREE four _one_ TWO three four
The most commonly encountered mnemonic for 4:3 is
Pass the gosh darn spinach
or variations thereof.