It’s no trouble!  I like talking about stuff like this, so it’s all good.  

I don’t have any experience with any sites beyond Society6, so I can’t speak for the others being good or bad.  I know there are some things I’d like to sell that Society6 doesn’t offer, like stickers (and Android cases again? they were for a while and I don’t know what happened), but the items I’ve received from them have been really quality and they have a lot of really good sales fairly frequently.   One of the nice things about the sales is that you can stack your artist discount on top of them.   When they had the mug sale the one day, I got like 60 dollars worth of mugs for 28 or something wild like that.  

 The trick with Society6 though is that you have to sell a lot before the numbers seem worth it.  I get less than five dollars for every item sold, and for most items it’s less than three.  I don’t know what percentage you get on any other site, but I can’t imagine it’s much different, honestly.   Also, you pay a dollar to sign up so they can verify your account.  This wasn’t a problem for me, but if you don’t have PayPal, or if you don’t have any money in your account right now, it might take a while to start. 

Advice-wise, I feel like it’s some generic artist advice, but a big thing is knowing what is going to work well as the particular item you’re trying to sell.  Not every image is going to work well as a shirt/mug/clock, so it’s wise to invest in making high-quality high-res versions of your work.  Society6 won’t accept things that aren’t a certain resolution at all, to their credit, but you can still make awkward things if you don’t take the time to prep the images.  Try to really sit back and think, “Would I buy this the way it is?” and adjust accordingly.    I tweak the images I use for each item to suit them as best I can, and for the shirts, I take the time to choose the colors that actually compliment the design, rather than leaving every default selected.  It takes more time and effort, but it shows a cleaner representation for your work and keeps you from being embarrassed when someone with no concept of color chooses something that looks terrible, haha.  My Andor shirt, for example, is only available on shirts in shades of blue, because that’s part of the joke, and I’d cringe if someone bought a red one.   

The designs are sort of the same way.  It helps to look at the things on Society6’s main page to get an idea of the things they choose to sell/that are selling well.   In most of my cases, I’m selling stuff based off of something that people already know, so it’s selling on that merit.  Original stuff, though, has to have another sort of appeal, especially for shirts, which a lot of people use to kind of advertise their personality and interests.   So it pays to take some time and put real effort into the images you prepare both in their content and their technical aspects.  Your most successful regular work might not be your most successful selling item.  It is maybe telling that my best selling shirt features a design that I created specifically TO BE a shirt.   It sells on other things too, but I sell at least one of my Garak “Especially The Lies” shirt a month.  

This maybe all boils down to garbage in, garbage out, haha.

Also, don’t be afraid to advertise!  I get most of my sales spikes directly after I put some effort into making a post on tumblr.  If you show a positive personality and have supportive friends on tumblr, they won’t mind signal boosting for you.   If people buy your things and you see them making posts, reblog them and share with your followers that other people have bought things, and thank the person who bought something!  It’s just a good practice all around.   It’s also fun to ask people what they’d like to see.  Sometimes what is an obvious want to your followers is not obvious to you.   (I would never have thought to do a G'Kar mug until someone pointed it out a little bit ago!  Now I’ll be making the next image I do of him specifically to fit that item placement!  I would have done a new DS9 painting much later had a follower not mentioned it, and when I did do a new one, I sold a dozen items featuring it in a week!)  

It’s good to take suggestions and combine them with your own instincts.  

I hope this helps!   Good luck with your future store, where ever you choose to base it!