Ghost is made up of 2 main parts: his core and his shell. I like to start by drawing a circle for his core and then adding guide lines for the shell. I draw one vertical line between his yellow triangles and a horizontal line through the middle of the circle.
After that, I draw an “x” where the 4 front sections of his shell meet and a smaller circle for his eye. Then you can add the triangles that frame his face. These triangles will help you place the lines and yellow triangles that divide each section of his shell in half.
Now you can form the upper and lower sections of his shell by connecting the yellow triangles to the “x”. The far sides should be a lot thinner than the close ones at this angle. Don't try to get the proportions perfect just yet. Focus on getting the basic shapes down first.
To form the next two sections, connect the ones you just drew to the horizontal lines. The left section is much shorter and ends in two tiny triangles. The right section extends outwards and ends in flat lines.
Once you have drawn all 4 of the front sections, you can add the back ones. The biggest back section looks a lot like the front right one and will eventually sit slightly higher than the one in front of it. All of the back sections must connect to the corners of the ones in front.
After that you can add the upper and lower sections in the back. These also need to connect at the corners.
Once your base is complete, you can start to adjust the proportions. If you are drawing digitally, lower the opacity of your first layer and make a new one on top. If you are using a pencil and paper, lightly erase your sketch to draw darker lines on top.
At this stage, I compare my drawing to the reference photo and adjust as necessary. This step usually takes the longest. It doesn't need to look perfect yet, so keep making changes until you're tired of looking at it and move on to the next step.
When you get tired of making changes, take a break and add in the final details. You can add as many or as few details as you like, but I always include the blue iris in the centre of his eye. You can also add the rings around his eye, the half circles on his core, and the little details along the lines of his shell.
Lastly, I like to make a few final edits. This is easier when doing digital art because you can add as many layers as you like. At the end, you can check if your proportions are right by drawing a box around him. If you turn him on his side, his sections should form a square.