While it is of course possible to paint directly from whatever subject matter excites your eye, preliminary compositional sketches and tonal studies can be a big help in solving problems that always seem to appear as the work progresses.
This applies to any type of subject matter – whether real or imaginary.
It is a good idea to keep all of your sketches – even ‘doodles’ – in file folders or notebooks for future reference when the mood strikes to attempt creating that masterpiece you always dream of.
While it is possible to sketch out a composition that looks to have all the elements that will provide a direct path to painting satisfaction, usually – after 2nd or 3rd viewings of those preliminary layouts or compositions, certain elements will look weak – or too strong, too light, too dark, etc. Just as it is a good idea to view your painting (in progress), using a mirror and viewing it in reverse over your shoulder, doing the same thing with your sketch compositions can be a big help in seeing possible trouble spots BEFORE you begin the painting process.
For example, here are three pencil sketches of imaginary scenes that were used for both watercolor and oil paintings over the years. You can find all three in final (painted) form on the pages of the fine art gallery.
At times, the desire to get right to work and NOT bother with all the ‘preliminary’ steps that will help insure a successful work of art will be hard to resist. When that happens and you succumb to that irresistible urge, I’d suggest you go ahead and ‘wing it’ and see what transpires. You might just get lucky and create a painting that will satisfy your artistic soul. I have on occasion beat the odds and created a nice piece right out of the box so to speak, but those ARE exceptions and do NOT often happen.
If you are working with transparent watercolor – and you ‘wing it’ without preliminary compositional (or) tonal studies and you run into trouble, odds are you will wind up with a less than satisfactory painting because of the difficulty in making any meaningful corrections.
If (when) trouble appears when working in opaque watercolor (gouache) – or acrylics, or oils, it is possible to (sometimes) overcome color errors, but compositional glitches, not so much. I suggest you NEVER toss, stomp on, tear up or burn paintings you consider to be failures. Keep them and use them as tutorials so that you will not (hopefully) repeat those mistakes. I have some such artwork that makes me shudder, but they do provide lessons learned.