pumpkin nail design will probably suit you better.
All you'll need for your skull nails is black nail varnish & a white nail varnish that has a thin brush. Start by painting all of your nails black, depending on how pigmented your polish is you may need to do two layers. When that's dry use your white polish to paint some teeth on all 10 of your nails by brushing four small strokes at the tip of your nail with small gaps in between each stroke.
Now you want to paint the skulls on one of your hands (I chose to paint them on my left nails as I'm right handed.) Start by painting a semi circle following your natural nail shape & then join the two sides together with a straight line above the teeth you painted. Finish it off with a straight line down the middle so that you have two eye shapes. When that's dry paint a small nose with the black polish.
For your other hand you can keep things simple (as pictured) by choosing a statement nail to paint the bottom jaw & ribs or you can go ahead & paint all 5 of your nails with that design. (I also experimented with painting the bottom jaw & some cross bones bellow which looked pretty cool too.) You need to start with painting a line bellow the teeth, leaving a small gap to all four sides, then using the tip of your brush (or a dotting tool if you prefer) dot as many dots as you can fit on your nail. My nails are cut short so I could only fit 3 dots but it's important to work with your nail length.
Finally you want to paint in some ribs to either side of your spine dots. Don't paint anything next to the top dot, just add some small stripes to either side of the rest of your dots. Finally seal with a top coat if you want your design to last & allow to dry.
The best thing about this design is that if you are a bit heavy handed with one of your stripes you can always wait for it to dry & go back over with your black. It's a lot easier than it looks & I think it's the perfect nod to Halloween without being too outrageous. I hope you like it, Happy Halloween.