This one's important, and it applies to pretty much any new endeavour: No one got good at anything by expecting to be great, straight away.
We know that visual thinking puts a lot of people out of their comfort zone. It can feel far more exposing than writing your thoughts down or keeping them in your head. But, the process of visual thinking is a uniquely powerful one, and it's one that, undoubtedly, requires a bit of courage.
So, when you pick up a pen and start to draw, don't make the mistake of expecting perfection. Let it be enough that you are creating a valuable habit that will, over time, enhance your ability to think, create, communicate and solve problems.
Beginner's luck is a wonderful thing. But hard-earned skill? That's far better.