Sketch and then keep it close!
The importance of sketching comes from the need of having a starting point. Basically it is a loose version of your idea, and it can be improved or put away for later use. I, for example, have some sketches that i did and that i like, and keep them close for inspiration. They are also good for my moral, when i think that i’m no good. Even when you have to work with a computer, you should make some rough sketches on paper, because it helps you visualize the idea you want to portrait easier and you can draw everything you have in mind quickly. Practically sketching saves you some time.
Also, when you sketch you are not that stressed up as when trying to do a final product, so your creativity will come naturally. Then scan your sketch and import it in your computer software and use it as you like!
It doesn’t actually matter if you know how to draw or not: the sketch is for personal use only, so nobody will criticize. For instance, when i want to do something in a software i make such a loose sketch that only i understand what it represents. So, it doesn’t matter your sketching skills, but your ideas that are put out to light!
As an advice, you should always have a notebook with you – mine is not even a sketching notebook, but a daily agenda, but it works with me!
Below are some sketches of mine – the ones that are my little help – some of them are characters for my future manga 
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I hope i’ve helped you even a little,