Hmmmm, seriously?
I have a strong suspicion what kind of answers you'll get below.....

It looks like your best sellers are quite different from one another. That should give you some idea of how to proceed. I don't think doing thousands of slight variations of the same icon will bring you a very large increase in sales.

I was going to write a big long sarcastic essay about the secret thing we all do to get tons of sales on SS but that's just too much work.

Don't you think if there was some way to increase sales, other than the obvious** we'd all be doing it?

** upload good quality commercially valuable work on a regular basis.

I think there's another key to more sales which is relevant to this thread, on top of the 'upload more work and upload better work' advice, which I do agree with. Variety.

I tried to come up with some kind of math to explain it, but I was confusing even myself... but I'm pretty sure I'm right!

So you've got a picture of a cat and it sells 100 times a month. So you think hey, this cat vibe is the way to go, I'll upload another photo of this cat. But the thing is, you're very unlikely to then get 100 photos of the cat in pose A an 100 photos of the cat in pose B. The person that would have normally seen your one cat photo now has a choice of A or B. if they only wanted one cat image then they're not going to buy two just because two are available... they'll buy A or they might now buy B instead of A.

Yes, having another cat photo gives you (on average) a better chance of them buying one of your cat photos, rather than somebody else's, but I can't see you doubling your sales as a result of that.

However, if that pose B was a picture of a dog instead, that could result in an additional 100 sales per month. I mean you've got your cat image to appeal to the cat buyers and you've got your dog image to appeal to the dog buyers. If you have too many similar images then you're just cannibalising your own sales.

I'm not saying don't upload more stuff that's similar to existing stuff you have that sells well... choice is always good, but variety might be the spice of microstock. I can talk, as the majority of my stuff is space stuff, but I try and cram in a bunch of variety within that niche.

Anyway, I could be completely wrong, but I'm confident that a cat and a dog in the hand is worth two cats in the bush. Or something like that. 

I think there's another key to more sales which is relevant to this thread, on top of the 'upload more work and upload better work' advice, which I do agree with. Variety.

I tried to come up with some kind of math to explain it, but I was confusing even myself... but I'm pretty sure I'm right!

So you've got a picture of a cat and it sells 100 times a month. So you think hey, this cat vibe is the way to go, I'll upload another photo of this cat. But the thing is, you're very unlikely to then get 100 photos of the cat in pose A an 100 photos of the cat in pose B. The person that would have normally seen your one cat photo now has a choice of A or B. if they only wanted one cat image then they're not going to buy two just because two are available... they'll buy A or they might now buy B instead of A.

Yes, having another cat photo gives you (on average) a better chance of them buying one of your cat photos, rather than somebody else's, but I can't see you doubling your sales as a result of that.

However, if that pose B was a picture of a dog instead, that could result in an additional 100 sales per month. I mean you've got your cat image to appeal to the cat buyers and you've got your dog image to appeal to the dog buyers. If you have too many similar images then you're just cannibalising your own sales.

I'm not saying don't upload more stuff that's similar to existing stuff you have that sells well... choice is always good, but variety might be the spice of microstock. I can talk, as the majority of my stuff is space stuff, but I try and cram in a bunch of variety within that niche.

Anyway, I could be completely wrong, but I'm confident that a cat and a dog in the hand is worth two cats in the bush. Or something like that.

Yep if on those rare occasions I have a good seller I try and load things that have some similar characteristics but not similar images e.g if its a cat at cat in a different pose or a dog in the same pose. I think it may be also worth revisiting a theme say after a gap 2-3 years. Apart from anything else I want to enjoy doing this ;-)

This cat-dog is good theory but I'm not sure, it works. For example, I uploaded a vector set of some chemical warning signs, and it was selling really well, so I thought I should make another set with some additional warning signs, thinking, if buyers see and download first set, they will for sure download a second set with more (similar) signs so I'd get double sales. Well this wasn't the case, it very rarely happened, that buyers downloaded both sets.
My conclusion: buyers wont download files that don't need. So if they need a photo of a cat, they most of the time will not also download photo of a dog.

At least that's my experience.

The thing is, my second set was also selling well, but buyers who downloaded first set didn't download second, and buyers, who downloaded second set didn't download first one. It happened that both were downloaded, but was extremly rare....

if you have an icon and it sells well, make more variations on that icon and you will have found a niche.

when you know what sells, make more of that. it works.

make sure your keywords are accurate and unique.