Cuttlefish are fine to eat. A few people prefer them over squid. You tend to get a triangle of meat rather than the rings though. No stingers, but beware of the beak.

To prepare squid I rip the head off, pull most of the guts out, then pull the quill out. (Having a bucket of water nearby is good to clean your hands/the squid/ink). Then slide my finger under the wing and the tube (you can feel they're separate bits), then slide down separating the wings. If you do that to both wings, the whole skin comes off very easily (unlike fish and chip squid rings which seem to still have the skin on). If theres guts you cant get, i turn the tube inside out to clean. Then slice into rings. The wings are fine to eat (you dont need to remove them, it just makes neater wings). Leftover wings, you can kinda pince between your fingers and palm and the skin comes off pretty easily. 

the easiest way is to rip off their heads, slice open the tubes, and then throw the whole lot into a scaler bag, quill, flaps, ink, and all.

tow the bag behind the boat in the prop wash until they are clean. job done.

you dont get rings from this method (i prefer to slice open the tubes and score the inside anyway, then cut into peices 5x5cm), but it is MUCH MUCH MUCH cleaner, and easier.

this is how i do it... in the kitchen

1. remove head from hood by pulling

2. remove quill inside the hood

3. divide wing from hood, and pull away wings - skin will peel off too.

4. run hand down the hood to squeeze out inside guts.(can use knife)

5.cut head from tenticles just below eyes

6. remove beak

I use a strip of plastic 2 inches wide and 1/8 inch thick,at one end it is rounded like the shape of a love heart.Holding the squid push the shaped end of the plastic down the back of its head inside the tube.This separates the guts from the squid tube allowing you to clean it without breaking the ink bag.Once the head and innards drop out you can do as described in previous answers to get the skin off.
The feather comes out with the head.Just nip the ink bladder off and freeze the head/tentacles for bait or cut the beak out and mince it all up to make squid patties,real good eating and next to no ink or wastage

the easiest way by far is the method i use
this method works just as well for fish so its worth practising
step 1, catch squid/fish etc
step 2,put in slurry in esky
step 3, upon arriving home remove esky from boat and put in garage
step 4,NOW THIS IS THE REALLY IMPORTANT BIT

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Call out nicely to wifey,daaaaaaaaarrrrrrling i have got some lovely fish for you, there in the garage,looveeeeeeeee youuuuuuuuuu,,
works every time no worries
please note if the garage starts to sting of rotting fish after a few days your method may need a little refinement.

Thanks All.