I was just about to post pretty much all of Rewth's advice, but he beat me to it

I'd have two additions though:
1) Round the corner of the skull's left eye. Skulls with facial expressions tend to look too modern and cartoonish for the game's setting. Rounding the eye socket will make it look less like it's raising an eyebrow at you. To the best of our knowledge, skulls didn't have eyebrows to lift in 1720
2) You might consider removing the fangs as well.
Happy drawing! It looks like you'll be turning out first-class sails and flags in no time.