So something that I admit I am struggling with is finding the right image for banners. I feel like when I create a batch of banners, I have no idea how each image will perform.
For example say if Im promoting a milf offer, I'll of course find images of Milfs to use, but I admit Im not really sure what Im looking for in an image that will convert well.
I'll use basic guidelines like "not too hot" and "amateur style" photos, but beyond that I feel like Im throwing stuff at the wall hoping something sticks.
So some sample questions I think of:
Nude or Non-Nude?
Close Up or Far Away?
Busy Background or Profile Shot?
Blurry/Fuzzy or High Quality?
Skinny/Fat or Younger/Older
etc. etc. etc.
I know I always have to test, but I feel like I need to have a better idea of what Im looking for. Often when I'll test images from banners Ive ripped, if they perform well, I'll really have no idea why as often these images will just seem random in nature lol.
I guess Im trying to understand on a deeper conceptual level what makes for a good image.
Any help is appreciated!
The scientific method comes to mind.
So, if a particular image is converting well, you can speculate WHY it's working so well, come up with a list of reasons, then test them out.
For example if the well-converting image is a woman of a certain age, ethnicity, body type, body position, hair color....then you can test other images that share one or more of these attributes, to see whether they'd perform well or not, and go from there.
Your list of attributes is a great start:
It's really hard to answer this question, often it comes down to testing one aspect at a time, following a similar plan as Amy outlined for you already.
There is nothing like a one specific type that you should be looking for... sometimes it's the face, sometimes the body, sometimes the way she is dressed, sometimes it's the location ... it all has just one thing in common, it has to look natural and believable.
For example a bit chubby lady with not so perfect hair and not so sexy clothing, but wearing something tight that reveals her curves, on a photo that shows her doing laundry ... that will work better than a staged model with fake DDs, miniskirt and perfect makeup. The first one looks like she might have a problem finding a partner in real life, cause she's busy taking care of her household ... while the other one will obviously be busy with turning offers for sex down all day long 
Thanks for the help guys I really appreciate it.
I guess back to the drawing board 
just a little add on, use the spy tools when you are lost about the actual idea and take the essence of it. see the themes that work, I like to see track record of time displayed.
if it works so long for an advertiser when he's paying for it probably means somethings working there.
banal, but always true