First off, let's start with a simple youtube video that I found that I think showcases a really simple and awesome nautical nail art. Just follow along and you'll have a really cute nail set in no time!
I've done a ton of different designs when I create my own nautical designs. I've gotten really creative and drew full on sailors and damsels in distress before, as well as whales, sandcastles, ocean waves, anchors, ships wheels, boats, sailboats, fish, starfish, light houses, coral reef, whales, you name it! Growing up near the ocean gave me a profound appreciation of the sea, and even though I don't live near an ocean anymore, I'm really hoping to again soon.
Although most people would stick to blue, red or white when making nautical designs, a lot of colors work just as good and can look even cuter! Pinks and greens look amazing with these types of designs, and you should definitely try out as many different combinations as you can!
I find a lot of what makes nautical nail designs so amazing to me is the little details you can add to them to really spruce them up. Just like the nail art above used the little gold buttons, I've added sand glitters to my nails, or even tiny seashells! Other than actual pieces to put on your nails, you can also draw on little contrasting hearts or whatever you want, it all works so well!
So give nautical nail designs a try! I totally recommend them! As for inspiration, check out the tumblr I mentioned before, or you can try http://brushonyou.com as they have a large selection of nail inspiration too!
Good luck everyone!