Start by drawing the body structure.
Draw a line like this for the body and legs.
The legs and body lengths are about the same.
To create the upper body, draw a rectangle around the vertical line.
Then separate the rectangle into thirds by adding two horizontal lines.
The head makes up one third of the rectangle, cap included.
You need to draw an oval for the head.
Draw ears on the cap, like this.
Now draw the legs.
Note that they're not jointed at the knee, but slightly curved instead, like this.
The arms start on the same level.
Like the legs, the elbows don't bend.
Now, the basic structure is done.
Draw the backpack.
Now you need to add some detail to the body.
Draw the arms like this.
Finn only has 4 fingers on each hand.
Draw the shoes, like this.
Their design is quite simple.
Draw the trousers.
For the face make 2 big black dots for the eyes, and a simple line for the mouth.
In most cases, Finn’s design doesn't feature a nose.
Now erase any unnecessary lines.
Then start refining your drawing by darkening the lines.