The key to improving textures or creating new textures mostly require some skills with graphic software like photoshop or whatever software you have. There is a free version of photoshop that is called GIMP I think if you don't want to buy photoshop. There isn't really a tutorial on how to create textures, like there is for creating weapons in blender. I guess every modder pretty much develops their own technique. The art of creating textures is much more free than creating models so there are millions of approaches in creating textures unlike 3d modelling. So I would suggest trying out some graphic software [like photoshop] and see what it can do for you, maybe try out some tutorials that you can find online [google knows where to find everything

].
Basically what I used to do in the past is first think of what you want to make and then look for a tutorial on how to achieve the material look. Don't think of tutorial as in like objects like "how to make a sword texture" but instead think of what the material would look like so look for "metal textures" instead for the blade and for example look for "wood material tutorial" for the handle for example [I'm just saying something...]. Also the best way to get realistic textures is to use photographic material. You can easily get high res pictures on stock websites that you can use for creating certain surfaces. For example if you need a concrete texture look up some pictures on stock websites instead of spending days creating a concrete texture from scratch and ending up with something that doesn't even look realistic

. Look at original Skyrim textures and see what they look like to get the same look ingame so your texture blends in nicely with the rest of the vanilla graphics and doesn't stand out too much. I guess if you learned how to model you can also learn how to make textures
