I will recommend you do a lot of reading in this forum for different techniques, wording, suppliers, pricing tips, legalities and a whole bunch more info.
You also need to find your niche market and plan to target them accordingly. The clothing market is extremely oversaturated and for every niche market, there are usually many brands trying to get those sales.
I would recommend finding a brand you like and breaking that brand down in the many different aspects of what makes them special. From branding, to social media interactions, pricing and such.
What you want to do is simple but extremely difficult, you want to beat them at their own game. Therefore you will have to spend lots of time studying others and learning what to do and what not to do.
When it comes to artistic type of apparel, direct to garment printing(dtg) will probably give you the most detailed options. There are many good dtg printers in this forum, I myself have been in talks with treefox2118 for some dtg services and he seems extremely reasonable with his pricing.
Search the forum for different techniques, think about which one will work best and then dig deeper into the suppliers, printers, pricing and such.
Good luck!!
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