Size of watercolor paintings
So what is the difference between simple watercolor paintings and difficult ones? The biggest difference is often the size of your painting. The smaller the painting the easier it is to paint with watercolors. The reason for this is because the greater the area of paper you have wet at any one time the faster you will usually have to paint before the paper dries so much that you risk creating mud if you keep working on it.
So if you are just beginning as a watercolor artist and you have found yourself struggling then why don’t you try painting at half the size of your current paintings? This is a quick way to give yourself a whole collection of simple watercolor paintings for you to work on.  If you have been trying to paint on a quarter sheet (14.5†x 10.5â€) then try working on an 8th sheet (about 7“ x 11â€) or smaller. You will be surprised at how much easier you find it.
When I have new students, their first few paintings are actually about 16th sheet size ( about 5.5†x 7â€) then once they are comfortable with that size I move them up to 8th sheet before going on to quarter sheet size. If I find them struggling at a larger size I encourage them to work smaller again for a while.
Simple watercolor paintings – demonstration
I have a demonstration painting on this site of a boat and sea scene which can be either a simple watercolor painting or a more difficult one purely based on the size of painting you want to tackle.
Try painting it at 16th sheet and then again at quarter sheet size and you will see what I mean about the relationship between the size of a watercolor painting and its difficulty. Painting the water component of this painting is done using the side of my brush to create the texture needed to give the impression of glitter on the water. This is done without too much water on your brush which means that the risk of the surface of your watercolor paper drying too quickly increases dramatically with size. The demonstration can be found at this link: Watercolor painting of boats and water .
This is also one of the reasons larger watercolor paintings are usually priced quite a bit higher, not just because they are bigger and have larger frames but because they genuinely take more skill to be successfully completed.
Painting small also makes you less concerned  about the time and materials (watercolor paints and paper) you feel you will waste if the painting does not turn out to your liking, though really no painting is ever wasted as you can learn as much from your failures as your successes!
Obviously there are other things which can make up simple watercolor paintings, such as fewer objects and colors, simpler shapes, less detail, restricted tonal variety, etc. However the biggest factor I have found which makes certain paintings more doable for beginner watercolor artists is reduced size! So if you are finding your watercolor paintings a challenge why not try painting them quite a bit smaller for a while and see how you go?