We had a great question in one of our livestreams recently that I thought deserved its own video. The artist was having trouble with their work looking too much like cartoons and wanted a more realistic look. This reminded me so much of when I started painting, it was a problem I had and I had the exact same question.
While there are a lot of things that can contribute to this, I find there to be three things you can adjust to avoid this problem.
#1 – Stop trying to include too many elements in a single painting when you start painting.
If I could go back and give myself some advice, this would be a huge one in correcting the cartoon look. I was so focused on creating a large painting with 80 different things going on that I wasn’t focusing on the things that mattered more in achieving my goal of a more realistic painting. I was completely ignoring my contrast and values.
When starting off you will be more successful if you can focus on one thing at a time. In this case, I would say paint a single flamingo on this canvas, or a tiger’s face, or a landscape. I was too new to painting to manage to get this many small elements into a single painting AND focus on values, lighting and everything else needed to make the realistic painting I wanted. By the way…why is the flamingo bigger than the tiger?
Now that I’ve painted and drawn several close-ups of flamingos and tigers in a photorealistic style, I have the understanding I would need to tackle a concept like this with so many in one piece. I now know where detail is important and where lighting and shading are what needs to be focused on.
#2 Creating Depth
The next problem I had was creating depth in my work. This was a problem in ALL of my paintings at the time. Everything in the back was just as detailed as what was in the foreground and my values were almost always the same. I had no concept of softening outlines or adjusting lighting and values to make things look softer in the distance. The birds, rocks, and plants in the distance should not be nearly as detailed as what is up close. If we look at the painting with the scene inside the mirror, notice how much more detail I have on the items on the shelf and how everything fades out the further back into the scene you look? This is something you can do to help avoid scenes looking too cartoony.
#3 Values 
If you want your work to look like a cartoon, then, by all means, paint the subject all one color. Tiger…paint it all one shade of orange. Flamingo? All one flat shade of pink obviously! Better yet, go through and outline your work to make it even more cartoonish!
Cartoons are one perfect color and outlined. Real life is not. Look at the flamingo in that first painting, then in the one below. No outline. No one shade of pink. There are SO many colors in this bird. Pinks, oranges, grays, reds.
The first few years that I was painting, I seemed to believe that more detail meant more realistic. It doesn’t. The biggest factors in making your work look more realistic are your lighting and shadows and your subject being drawn correctly. If I were to make changes in how I worked when I was younger, I would have spent more time focusing on smaller studies. The faces of animals instead of a whole scene filled with a group of them. It’s not that you won’t go back and paint full scenes, but I think that it’s easier to tackle if you start with the close ups then work your way back to larger scenes.
I was brought in to fix a mural many years ago. The first artist had painted the subjects but used all midtones. No lights, no darks. Everything was safe and midrange. Safe and midrange tones are flat. The only thing I had to do to fix the complaint that the first artist painted everything too cartoony was to take my airbrush and add deep shadows and some highlights on the subjects. The first artist hadn’t really done anything wrong…but she was calling her work, what I would have considered an underpainting, finished. It needed shadows and highlights! That one adjustment made the client happy.