I currently am working on a project to make a realistic render of a bunch of fir trees planted in the shape of an american flag. What things can I do to make this look more real to life? I have GA on, I added some haze, wind, and the hills all have ground that is just bumpy brown colored. They also have carex at around 90% populated on them. Is there any other effects I can do?

If you really want realism, go for global illumination instead of global ambience. Much more realistic. You'll need solf shadows for the sun as well, like 5%. I would add some procedural grass to the hills mat, to have more variey on the ground, and drive the mixing of materials with a fractal function.

To be honest, I hate using the Vue fir tree.  It just never seems to have much depth when rendered.

Try GI though...and maybe slight variances in color

I agree with the fir tree looking not so great. Are there any other pine trees out there that support wind?

There are two conifers at C3D you can check: the cone shaped conifer and the bulky conifer. They are not fir trees, but they look really good.

I might get those. They just have to be close to a fir tree. Any conifer that would grow in SD works. Thanks! Any other tips?

Global illumination is the way to go if you want realism. You can try and create a custom volumetric atmosphere, but it will add to the render time.

Not much else to say.

PS: GI quality slider can be set at -1 to speed up the render without quality loss most of the times.