Further to the previous post – this is something I leaned from my second-ever piano teacher:
Have a look at this Clementi sonatina:
Anyway, what I do is practice releasing the first left hand note when I play the second note of the right hand. The same happens in the next bar. In the third bar, I learn to release the left hand notes at the same time that I play third and seventh quavers in the right hand. And so on and so on, throughout the piece.
That way, the crotchets in the left hand will always be exactly the right length in relation to the right hand melody.
This principle can be applied anywhere there is a detached accompaniment to a melody, in either hand. Because this “learning” goes into the “muscle memory”, it will stick, freeing up brainpower to focus on other vital elements of performance.