Making an outline for your creation can seem quite simple. And yes, you are right! It is! But you can also use some very simple techniques to add variety to your drawings.
All lines don't need to be the same size or colors! Adding a ticker line on some part of your drawing will put emphasis on it.
You can also play with colors. The outline doesn't need to be exclusively black. Drawing an outline in a different color than black will help the reader, for example, distinguish your character more easily from the background.
However, be careful to not overuse this effect. It might look more ridiculous than effective if not done properly.
You can also use a mix of black lines and... no lines at all. If your character is near a very intense source of light, then you might want to try not drawing any outline at all.
This will increase the visual effect an intense light would have on a character, just like in real life.
I think that most artist don't really use all the advantages of an irregular outline, whether it is created with colors or the thickness of this line. Learn to play with your outline and your drawing will have a little something that most cartoons don't!
Example of a drawing with an irregular outline.