The best way to understand how to sing and play any instrument at the same time – whether that’s a piano or a guitar or something else, is to understand clearly how we play *one* instrument on its own. The answer is, we sequence. Our memory associates playing the first note with the fact that the second note is imminent and then associates playing the second note with the fact that the third is imminent and so on… In the case of playing piano, we use two hands, so the first and second notes (or chords) may be executed with the left hand while the third occurs with the right. As a consequence, we have to switch our attention between the two – if not visually then at least with our proprioception.
If you are singing as well, it’s no different. If the first and second things that happen occur with your left hand, the third with your right and the fourth with your voice, then you basically have a list running in your head of all the things that happen with your left and right hands, mouth, breath etc. Ultimately it’s repetition that will make this list really flow. Then you can focus more on relaxing or expressing yourself emotionally – usually both deeper desires than acquiring musical technique.
The next question forming in your head should be: how do I acquire this musical list of actions? Well if you read music proficiently then that will help a lot! You can literally see on the page what happens and when. Then you just play/sing everything slowly (separately at first if you have to) until you get it into muscle memory and your body does everything automatically. Even if you don’t read music well and play mostly (or completely) by ear, I’d recommend learning well enough to notate short passages that you find challenging in order to understand this interaction between the voice and the instrument.
What you are looking for is a clear picture of the combined sequence of events executed by your instrument and your voice. You could get to this by jamming and trial and error alone but slowing things down, thinking about them, writing them down or even reading someone else’s notation are all worthy shortcuts. A good tip also, is to use the techniques you are more familiar with to gain understanding quicker. For example, if you are a competent pianist but less confident with your voice, try playing one hand of the piano part and playing the vocal part with your other hand. This helps you understand the sequence of events that need to take place. You can be creative and think of other ways to swap around your tasks so you can learn them more easily.
Above all, don’t lose hope! Playing and singing as a learnt process can be extremely challenging but it’s never an impossible task, no matter your skill level. You simply need to have the persistence to understand how the instrumental part interacts with the vocal part and then practise it as you would any other performance. It’s a finite and logical process. Really, there is no magic to it! It just looks and sounds like it when you get it right!
ps. The principal’s exactly the same on guitar and piano. Check out this performance linked below to see all the techniques above in action.
All the best,