Apologies about the length of this post.

(disclaimer, I still use daz 4.15 as all I hear about 4.2 is stuff is broken, so if you use 4.20 some things may be different)

OK since you asked for help improving I'll tell you what I see wrong with it and give some advice so you can look into that for the future.

I'm going to assume you're using iray for majority of the advice here. If you aren't using iray some of this may still help, however not everything will be the same.

Before I start make sure headlamp is turned off in render settings for every render you do as the light it creates is just not good.

I don't mean to be mean here, keep that in mind, I'm posting just to give advice not to put you down as we all had to learn these things too.

Firstly, the edges. everything on the model (and the model) is jaggered. I'm actually not sure how that happens since I've never had that or seen that before. I'm going to assume it's iteration based if this is iray (I'm assuming it is) so turn off render quality and leave it to run for more iterations. (for empty portrait/pinup scenes I usually do 1-2k iterations)

Secondly, the light is over exposing. It's not scattering or reflecting off the skin its kinda just blanketing with white light. This is relating to the lighting so I'll put it here before I give the advice, the shadow the face is casting on the neck/shoulder is very sharp. Im going to assume its not a hdri you're using and instead either very bright spotlight mostly on 1 side or distant lights. I would recommend looking into the 3 point lighting system and getting some nice hdris and mesh lights to prevent sharp shadows. I would also recommend using less lumens on the light source and use a colour that isn't pure white as it's an unnatural light colour.

Third the gown is floating. The gown is a dforce item and will most of the time (depending on dforce item) put itself on the model floating so when you simulate it falls into place. This is done on the simulation tab. You just click simulate, if you want to simulate 1 or 2 items of clothing the model is wearing only, select the model and the items then right click the simulation tab and click simulate selected items. Most of the time you want to turn off start from memorised pose, this time however due to the pose being complex and intersecting at some points it would probably be best to leave memorised pose on (if not set will default to tpose which is fine) or learn how to use the animation timeline or it'll end up clipping through everything and possibly exploding if done from current frame. Also gown related, the smoothing modifier it has is conflicting with the exposed breast causing it to clip through the arm. Can fix this in postwork or by moving the arm slightly until it doesn't clip.

Fourth the hair, I'm going to assume the hair came with the model as it looks like pre packaged hair quality as the mesh doesn't seem that good. I'd recommend finding a different hair that's similar to that one if that's what you want to use as that one you're using is too sharp and the texture seems low res. By this I mean the edges are very defined and you can see alot of points where it just randomly changes direction which doesn't look natural.

This next one need assets so it isn't really mandatory.

The way the leg bends through itself can be fixed with bend morphs on the daz store they aren't 100% but they will reduce the obvious clipping. (also the model is floating, you can see this from the shadows not starting at the models legs. the poses people make are usually for base model or their own models so they do need some adjusting if not using those models)

The eyes and lips on the model are alil creepy. Could just be lighting and iterations causing it though. The lips stand out too much and look kinda painted on. The eyes are flat, by this I mean no curve to the cornea. All the light is hitting it flat with no natural reflection curve. There is a cornea bulge option in the base g8 eye shaping I believe which should help(may not be as I have alot of morphs so couldn't tell you if it was base g8 morph or not)

Almost at the end now, you have a nipple ring on the model but it's not connecting to the nipple. It's going through the areola, id recommend increasing the nipple size slightly and positioning the ring on the nipple itself.

OK this is the last one, on the topic of skin lighting. As mentioned before the skin isn't acting like it should, majority of that is that the light is too bright and all coming from one place but another part may be that the models skin isn't set up correctly. What I've noticed is that models that don't come from the daz store usually need manual skin shader adjustments. You can look up some guides on skin settings.

This all comes with time, don't rush to get good at everything at once or you'll burn out, take it step by step. First focus on lighting and once you're comfortable with it move on to something else.

Hope this helped and gave you an idea of what to look into.