Go the extra mile with your art files
When it comes to selling your art, especially on print on demand websites like Society6 and Redbubble it pays off to take your time and create as many file options as it requires for your design to look good on a product. Why? The plain obvious is that you maximise your chances of getting a sale if you do it, but when it comes to your long term career, it will show a lot more professionalism if you take the time to go the extra mile, no matter how tedious it might seem at first, and I get it, with some platforms, it can be a drag. Society6 being the most famous for lengthy upload procedure among artists because they don't offer the option to tile a design or alter a background color in their artist studio like several other PoD do. For me, this usually mean uploading an artwork and all it's variants can take over an hour at time, especially when I need to create new files to fit certain products as I go. But it's totally worth it in the end. The way I see it, it's a good way for them to separate the wheat from the chaff so to speak. serious, dedicated artists and surface designers are more likely to put in the extra work than the ones who tend to see those platform as a quick and easy way to make money (which it is not).
go in for the long game
I'm pretty sure all of us seasoned commercial artists and designer have at one point or another decided to start with Society6 or Redbubble as a side gig or a launch pad for something more while we figure things out.
The thing is the earlier you start treating it as a serious business, the more you'll get out of it if you really go all in and really go the extra mile with your art files. It's especially true with Society6 which has Deny Designs as a sister site, which is a company that only deal with whole sale clients and counts Target, Nordstrom and Urban Outfitter in their rank just to name a few. Artists who keep showing up, and put effort into their work are more likely to catch their attention. Not to mention that several media and retail companies also look at Society6 and could spot something they like and would love to license.
I see it a lot in questions on Quora where I actively participate and write answers. People are usually asking how they can make money with Redbubble or how can they sell quickly, or ask if selling on PoD is profitable at all. The answer is that it's not quick and easy money, but yes, it's profitable if you put in the time and effort into it, and it starts with quality artworks and files.
I usually create the same standard 5 files to begin with when I turn an illustration into a sellable design :
1 JPEG art print file, usually 24 x 30 inches at a 300dpi resolution
1 Square 10k x 10k pixel JPEG file with the illustration in the center, this is so that it goes on larger products with enough margin to resize without cropping the artwork, and it works as a square mural file on Society6
1 seamless tile file at 3600 x 3600 pixels, this is to go on the wallpaper on Society6, and can also be uploaded as is and tiled directly on Redbubble to fit certain products. Now That I sell in more place, that seamless tile file becomes handy to sell my designs as fabric on Contrado and Raspberry Creek as well.
1 large pattern square, I usually create tis one solely for Society6 because they do not have the option to tile a design in their artist studio, and the pattern file is my to-go to for curtains, and comforters in particular. I usually do a 12k by 12k pixels square and use my seamless tile file to fill it and create the pattern
Last but not least : 1 TRANSPARENT png file, where there is no background around the illustration. This file is mandatory to have your work printed as a kiss cut sticker or on dark colored t-shirts. On Redbubble where the hot sellers are t-shirts and stickers you can't do without that file, ditto with Teepublic which sells mostly t-shirts. For this one I usually remove the background from the art print file and I am good to go.
Then there are all the specific sizes that work for certain products like table cloths, Apple watch bands, yoga mats and outdoor floor cushions on Society6. Society6 actually has a LOT of products for which you are often better off designing an entirely new file. Sure you could slap the pattern file on a lot of them, but sometimes, just going the extra mile works beautifully and I urge you to spend those few extra minutes to do it.
Some of their products have the option of downloading the psd (photoshop) template so you can create a design that looks just right on that less straightforward product. Duffle bags, backpacks, leggings, socks and floor cushions are all products were you should explore the possibility of creating a separate file if the pattern square won't do, or quite frankly another option would take your product from "fine" to "wow". This is what I did with the bench in the picture. The pattern file would have looked acceptable but a bit too "vanilla" for this design, so instead I made a file specifically for the bench and put 2 sea turtles facing each other. It took about 5 minutes to create that file from my existing assets, and a minute or so more to upload it. I frequently do it with outdoor floor cushions, coffee mugs and yoga mats, because those really benefit from taking a few extra minutes of my time to create a special file. The bonus is that some of those files work on some of the other products Society6 has to offer too and you only need to upload the file once with them, after that it shows in the asset library for that specific design, which comes in handy when they launch a new product, about 90% of the time, one of the existing asset uploaded will work on the new product.
Out of all the Print on Demand websites I sell with, Society6 is the most demanding when it comes to art files, so I always create my assets and upload them first with them, and then with other PoD platform because chances are the files I created for Society6 will work almost everywhere else without me having to create anything extra later on. Back in 2017 I started with just Society6 and Redbubble and now a quick glimpse ate my shop page will show you how it expanded from there over the years.