Today, i went out shooting to do this.
Rebecca R 
I will try my best.
For me iso 100 is the best that my D80 can have. some DSLR can do ISO80. ISO 100 helps prevent grainy or noisy photo. but even at ISO 100 if lighting is not good it could still come out noisy. one way to help get more light is lower shutter speed. like 1/60s. but it will be hard to get a sharp image since a slight movement with make photo blur.
here's a sample of me not using ISO 100. you will noticed the photo has noise and details is less.
Model NIKON D80
Shutter Speed 1/200 s
F-Number f/25
ISO ISO 320
Exposure Bias Value 0.00 eV
Metering Mode Spot
Flash Auto, Fired, Return detected
Focal Length 60 mm
Lens Model 60 mm f/2.8
White Balance Details Auto
Date/Time Original 8/22/2017 11:17:16 AM
Model NIKON D80
Shutter Speed 1/200 s
F-Number f/25
ISO ISO 800
Exposure Bias Value 0.00 eV
Metering Mode Spot
Flash Auto, Fired, Return detected
Focal Length 60 mm
Lens Model 60 mm f/2.8
White Balance Details Auto
Date/Time Original 8/22/2017 11:17:46 AM
you will noticed that the 1st picture with ISO 320 has less noise and more details. i did not adjust any of the photos exposure and sharpness. i just resize them. so that's the actually shot from dslr.
here's iso 200. my DLSR is okay upto iso200. but for macro. i must set ISO100. otherwise i will most likely delete the shot.
this one has ISO110. i cropped and adjust the exposure and sharpness. if i do it on a photo with high iso 200 and above. in macro it will show less details.
Model NIKON D80
Shutter Speed 1/200 s
F-Number f/16
ISO ISO 110
Exposure Bias Value 0.00 eV
Metering Mode Spot
Flash Auto, Fired, Return detected
Focal Length 60 mm
Lens Model 60 mm f/2.8
White Balance Details Auto
Date/Time Original 8/22/2017 11:13:07 AM
What my setting is for macro. always iso100. then try to change the fstop and shutter speed to get a good details and exposure.
ISO 100 shots will allows us to cropped while lossing less details. making the subject larger.
what if iso100 resulted in bad exposure.
- you can adjust the fstop. remember it will reduce the area of focus.
- adjust to slower shutter speed.
- if both fails a good external flash is needed
Honestly all the problems and imperfections can easily be solve by having a better gear. but what i do is max out my current gear features. Check it's specs. read and understand them. then start experimenting and shoot a lot. In time it will be easy to shoot. :)
i remember 2007 when i was starting. it's hard to shoot macro. i have the same gear setup then. upto now. D80, 60mm and sb800. results are 99% bad. if i got 1 good pic. i did not even know how. and cannot reproduce such shot. I was really confused and felt tortured for hours. I did not enjoy it. so i stop shooting around 2009. and restarted 2014.
Now all became easy. a good day with willing insects. a two hour time will produce 100+ 75% good photo to share. That's how i enjoy my photography hobby and with steemit. It's more interesting. Am still learning how to do better shot. I did stopped but never gave up :)
Going back to Rebecca R. I hope i was able to explain.
Hope this tips helps.
ps. feel free to ask and will try to assist. thank you