I don`t know the song yr talking about and I`m slightly confused about the exact rhythm u were trying to describe. U mean straight triplet as in 3 quavers? Or excatly what kind of value are yr triplets in? And semiquavers as in 4 semiquavers?
So Lh 3 quaver triplets VS Rh 4 semiquavers? Was that what u meant?
Well, anyway, no matter what the rhythm distribution or value was, all u need to do is to practice em seperately (in the first place) to a uniform pulse. Ie: U may wanna feel the stronger crotchet pulse/ play em to the crotchet or something like that.
Then, just put em together, and all the time, following the crotchet pulse. It may sound absurd, but learning to feel the pulse, and feeling them evenly is the easiest method. U may try tapping the rhythm simultaneously with yr 2 hands...upper stave with RH, lower stave with LH and so on. It`ll be easier to play once yr hands gets the so-ordination through the clapping ex.
OR, alternatively, u can take a pencil, draw straight lines and trace out where the notes will meet, or find their order. But I really don`t recommend this...unless as a last resort.
Caz, the feel of the pulse is the most accurate and natural manner. Imagine trying to subdivide with yr pencil, a group of 17notes against 5 or etc. in the future. It`ll be impossible...u really have to sueeze them in evenly to the same pulse.