To start, let's focus on the head of the octopus. First, draw two interconnecting egg-like shapes. Erase the lines to create one solid shape. Draw a small triangle jutting out from the left, about 3/4 of the way up and draw in some guides for the eyes.
Use your guides to help you start your final drawing, starting with a strong outline. Add some eyes and make them look cross by arching the brow ridges. Finish off your drawing with some markings on the back of the head and some lines going down from the eyes.
Next, the tentacles. Draw two wavy lines coming together to a point. Draw semi-circles inside your lines to hint at form.
Start on your final lines; add a broken line across the middle of your tentacle. Finish off by adding suckers to the underside; these can be simple squiggles.
Combine your head and tentacle guides to create a solid set of building blocks from which to create your final drawing. Add bubbles and wiggly lines to make it look like your octopus
is underwater.