Instead of looking for tutorials that demonstrate the technical stuff, you really should be studying the foundational knowledge instead–things like composition, perspective, lighting/values, color theory, anatomy/figure, clothing folds…etc. The technical stuff is a piece of cake compared to the critical foundations, and if your foundations are solid, it only takes a very short amount of time to become proficient technically.
Compositionally, this is probably a bit loose and could be tightened up a bit by making it a portrait aspect ratio instead of square. The scene itself doesn’t really need the extra space horizontally.
She is fairly attractive and her proportions are pretty good, so that’s plus.
The lighting is incoherent because you have your main light source back-lighting the subject, yet, the subject is very bright in the front, as if there’s another bright light source in front of her. To make the problem worse, that unexplained light source apears to be very diffused and coming from all directions, as if she’s in a photography studio with a bunch of photography lights all going off as once. In order to make your scenes credible and authentic, you must first decide on exactly what your light sources are and then stick to it.
She should have a clear rim light on her from the moon, but the rest of her should be much darker, pretty much a silhouette. If you want to illuminate her from the front, then you need to think of a credible light source–perhaps a torch light, a bonfire, or even magical light–anything but a nondescript diffused light.
Her hair looks too stuff, like dried hay. Taper your lines when you paint hair strands. Set your pen to vary brush size by pen pressure, and then practice drawing tapered lines–it makes all the difference in the world.
Her clothing doesn’t look credible because the lack of folds and wrinkles show you don’t know how to depict natural looking folds and wrinkles, but by skipping them, the clothing looks over simplified in contrast to the details we see in the rest of her.
This is one of the obvious drawbacks of using photo references as a crutch–whatever isn’t in the photo reference, you have a hard time painting out of your head, and it always looks less realistic/detailed/natural than the parts that did use photo reference.
The ocean looks too vague. The ripples and waves when backlit like that are actually very contrasty. Even if there’s fog/mist, it still wouldn’t look so smudgy. Instead, you should paint a contrasty ocean, then put a layer of fog/mist over it, instead just painting the ocean really vague and smudgy.
