I've been experimenting with different lighting techniques and wanted to hear your opinion on this image.

Also, how important are the use of shaders in your scene? I've never used them before, but I have tried

them once or twice and unless I'm doing something wrong, I didn't notice any difference in the results

once rendered. Is DOF a simple integration or is it a learned skill through trial and error?

Without a doubt IMO, lighting is the most crucial part in rendering a quality image that has realism.

Here's a sample render, any thoughts or tips on what I could or should do with this particular image

to increase its realism?     Thanks guys.

How close to real do you want it?  I quickly took an overview of your render and noticed several things that would need to be addressed.  As you mentioned, DoF is a major component.  A sharp background in a portrait is very distracting and takes away from the main focus of the image.  

The lighting in the background shows either a setting or rising sun.  Usually, the color temperature is around 3000 - 4000 degrees Kelvin, a warm yellow-red to orange color emission.  You can see that on the outside of the cabin walls.  You may want that effect to spill over throughout the scene. 

On the model, the necklace is not casting any ambient occlusion shadows, it just looks like it's floating in midair.  Not very convincing in terms of realism.  There is a lack of skin texture detail, you can see that in her palm.  That might be a map problem or the primary light washing out the details.  

Your main light needs more adjustment, I gather that you are using it as a flash or portrait lamp to illuminate her face.  But I find it too strong because such a light would cast real shadows into your background.  Plus, there should be a light falloff into the distance, I don't see that effect in the trees behind her.  My recommendation would be to move the main light to either side of her face to cast some interesting shadows as opposed to the straight lighting you have now.  A backfill-colored light opposite the main light would separate her from the background better.  You would need to experiment with that.  

Soften the image, harsh details in a portrait do reveal imperfections.  

Question: is your background a static image or added props?

Ouch! JK, the tree on the right and close up foliage are props, the cabin is 2D wallpaper. I did this scene really quick so I knew there would be tons of flaws in it.

I wanted an overall opinion on those basics, and I appreciate your input on them. Thank you.

DAZ has made DOF a very quick and easy thing to do in Studio.

It is also a good way to hide those other things you mentioned; mismatched backdrop lighting and untweaked material shaders.

In portrait shots, The focus is sharpest on the eyeball and the area of focus is kept tight. In this shot the area is so confined that the tip of the nose and the other eye is out of focus. In practice that would take an expensive lens to do.

The sin being hidden here is LaFemme, LOL.

Excellent points my friend, thank you for your input.

Everything everyone has said good and right,… but you said “...to increase its realism” your render is fine! And real! NOW before people start piling on; you said realism not photo realism; BIG difference. Some where on the daz forums there is a whole large (many post) topic on this, and one person who can really do great “life-like?” photo realism renders.

In life ‘realism’ everything is in focus. Your eyes focus, a camera is even worse, the ‘realism’ you(or other people) appear to want is the defects of the human eye and worse the camera. Like I said there is one person (in  the daz forums) who does the defects really good, flash and all. Photographers have all always wanted to go the other way where everything is in focus and then you can back and if you want ‘get creative’.

When I hear people say they want photo realism I know what they want, I don’t think they know what they want/mean.

Thank you for your input. What I mean by realism is basically that I don't want my renders (portraits specifically) to have that sort of 2 dimensional look to them.

I don't per-say want them to look like a "real" photo of a living person, but at the same time not to look like a cartoon so to speak if you know what I mean.

yes i do. jeff_someone is the person in the daz forum(sorry ren) but it is about helping people be their best-no?-. https://www.daz3d.com/forums/discussion/313401/iray-photorealism (sorry ren).
that is "photorealism", but not ~real~realism you don't have a bioflash growth. every image you have ever seen until recently, history wise; has been a photo; of some kind. now if you want 'realrealism' render your images in stereo.(pairs). without DOF.

As stated above DOF is very easy in Daz, and makes the world of difference, try downloading some HRDI's they make lighting a lot better and in conjunction with additional lights (or emissive planes, like i use) can also boost the scene, The skin on the other hand, is the standard Daz plastic, and i never use skins out of the box from anywhere, i have heavily customised mine so that it looks like skin, it has depth, not only in bumps but in lighting at different levels as light passes through it. Im currently thinking of posting my skin shader over at DA as Rosity dislikes my work (there is worse here) Rule one, Play with it and save often, sometimes you find something new and you become better, Daz is very easy software to use, i know, i use it, lol.

Also, the focal length setting will affect DoF slightly, lower values will give you a bit more wiggle room with DoF range. However, linear perspective will be stretched which sometimes is useful for moving the background a bit further back from subject and bringing peripheral objects into wiew. My personal preference is to use a focal length of 45mm to 50mm. Experiment with different settings for focal length, focal distance and f/stop.

The lower f/stop values will give you more blur but will reduce the focal range, higher values will do the opposite.

Also, the f/stop values in the Tone Mapping menu have no effect on DoF and vice-versa. I mention this as it has been a cause of confusion.

Good luck in your adventures with DoF and if in doubt, experiment.