Concept - what message do you want to get across?
Cute, feminine t-shirts for female developers. The designs should be cute and the print should glitz or be very colorful or plushy. I will try to spread the word via Twitter, Facebook and Instagram and when meeting other women who code offline (at work, meetups, conferences).
Type of shirt - how will this shirt be produced?
Mainly women's cut. But hey, I also sold one "eat sleep code repeat" to a man :D
Creative execution - how will you convey your vision?
I don't expect that high demand, so I have chosen and online printing vendor so that I don't have any upfront costs. Personally I love to wear black shirts. With DTG printing you don't achive very vivid colors on black. And I totally love glitz or plushy prints. So it needs to be flex and flock printing. The only vendor I know who does that is spreadshirt.com. You can order the shirt in any color you want, and the end-customer could also customize the size, location, print method of your design in their shirt-designer.
I also tested Redbubble with a DTG print, yellow on black (was a Star Wars Logo), female shirt - but was not satisfied, color is meh, the women shirts are quite pricey and I did not really love the shirt quality.
Cost - what will this cost you to make?
The tees from spreadshirt are quite costly when comparing them to getting a shirt yourself from a wholeseller and screen print it. But as I don't want any inventory, this is the right choice for me. I like their shirt quality and their support is outstanding. Thier premium t-shirt + printing is $19, so I charge $ 5 for my design -> the endprice is $ 23.99, which I think is ok for a unique, glitz, flex or velvety shirt.
I am really satisfied with Spreadshirt's flex/flock printing results. To print with those methods you'll need a vector file.
Check out my t-shirts
A special thanks to the creators of the free King Basil font which I use for my designs.
Pictures of my shirts
eat sleep code repeat - light blue velvety
hello world - two color flex print
code love - pink glitz flex print
developer - gold glitz flex print
nerd - pink flex print
Let me know what you think :-)