How to draw anything: Pay attention to details, draw from references.
First block out basic shapes and locations of things, then start outlining the detailed parts
Then either start with the darkest color and fill in the whole picture and work your way up with patches of light, or reverse, start with the lightest and gradually block in darker and darker areas.
I like these.
Draw squared-off-ish domes for the tops, then the lines coming out for the tentacles. Make the bottom edge of the dome wavy, like the frill. I would fill the image with the same blue of the background, here, and start paining with the dark purple/gray that you see around the top edge of the foreground jellyfish. Block in the dark shapes. Move on to the lighter purple/pink and block out those shapes as well as some of the tentacle-y stuff in the center of the tentacles. Then move on to the lightest pink and block out those shapes. Then smooth everything together with midtones.