Once the idea is clear, you can start making sketches.
I prefer sketching by hand, which gives me more precise control.

The amount of sketches I make varies, before I am satisfied. If it's my lucky day, the first one is good enough; if not, it can take a few more sketches before the result is good enough.
In some cases, the result will never be good enough, no matter how often I try. Once this happens, I realize that the point of view and/or subject is not right, and I have to think of a different approach and/or find some extra reference images. Or try it again later.
You need to have the right mental state for creative activities. If you end up stressed out a lot, usually this isn't the most ideal state of mind.

sketches of seascape
Sketches of seascape

If a sketch is used as a reminder, it doesn't need to be very detailed. I usually use a ballpoint for this type of sketches.
If a sketch is used as a visualization of the final illustration, then it should be more detailed.
Don't bother about the aesthetic qualities of your sketches, and/or the parts that are not well drawn.
For some extra information, you could write some text around certain parts, especially if the sketch is very roughly drawn.

The next illustration shows a selection of sketches I made for the IC-Project pixel art illustration.

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