Blonde's arm is way too weirdly posed. It's going through hairs of the blonde and her hand is going through brunettes hairs. It looks like her bones defy logic.
Posing: Don't be hasty to render and Always be sure that pose looks decent before going any further. Posing is something you will learn the more you do it. But its good to look up about pinning while posing for Daz on youtube maybe.
Expressions: Don't fully apply an expression. Mix them with different dials. For example, I use Subtle smile dial by 25% and Pretty Smile dial by 50% and when combined it turns out really nice but if I use only a pretty smile dial 100%. it looks monstrous. (These dial names are imaginative but it's the concept that you should pay heed).
Lighting: I can't help you much with that cause everyone has their own method of lighting but there is one very common technique used by a photographer called 3-point light system which you can emulate in Daz with spotlights. You should look up 3-point light in a search engine to see what it is. I myself don't really use 3-point system but it is an eye-opener and from there on you can experiment with lighting.
Rendering: Do not fully render a scene until you are very sure everything is perfect. You can make a quick 400-500 pixel 200 iterations render to see how it may look before seriously rendering it. That saves time.
There are more things I could tell but it's not good to try everything at once. There are cameras, shapes, instancing, Dforce, timeline, tone mapping, mesh lights distant lights, environment settings, shaders, and whatnot. If you keep on rendering long enough then you will probably end up learning all these with time.
These are very basic things to make some pretty renders. And here I present you a Render with nothing but a single spotlight which I created for a Daz challenge in February this year. Oh! Those clothes aren't real.
Maybe its just creativity and passion that creates good renders. Only one spotlight and it still turned out this nice.
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