It’s physically impossible for humans to multitask (see my post on multitasking).
Piano students seem to think otherwise. They don’t realize that solid right-hand and left-hand relationships are a result of building, shaping and maintaining an extensive vocabulary over a span of many years. We can’t focus and actively improvise with both hands at the same time. One handalways has to be on autopilot, even though it may be for only a few seconds. Therefore, your hands must have an intrinsic vocabulary to pull from while they’re on autopilot. They have to rely on muscle memory. Otherwise, your hands will only play what they know: nothing.
What do you do with your left-hand? Well, what’s your concept? You have to give your left-hand something to play first! Let’s say: a quarter-note bass line over the blues.
Side Note: How do you form a concept? By asking, transcribing and listening to the specialists!
Pick a twelve-bar, quarter-note pattern and stick to it. This is not a creative exercise. If you’re wavering from the pattern, you’re wasting time.
Practice it a million times. It’s all about repetition. Train your left-hand not to think. Learn it forwards, backwards, upwards and downwards. Learn it from the start, the end and the middle. Learn it in every way. Memorize the notes. Memorize how they look, how they sound, how they feel and how they taste. Learn to play it in your sleep. Know it better than anybody else. Own it. Add your right-hand. Experiment with different melodies, rhythms, tempos and improvisations. Try to throw off your left-hand. When you’re comfortable, move on to the next pattern and repeat.
This process achieves two things. First it develops your muscle memory and vocabulary. Secondly, it rids your playing of bad habits. But only if you’re disciplined enough to stick to your patterns and immediately fix any mistakes and inconsistencies. Again, this is not a creative exercise. You’re infusing vocabulary into your muscles. Creativity would be an act of blending vocabulary. That doesn’t help your left-hand autopilot. The whole point is to think creatively with your right-hand!
Of course, for future study, try putting your right-hand on autopilot!