As for what to avoid, well, it’s a case of keeping it legal. Don’t infringe anybody’s copyright, and be sensitive to other people’s feelings – remember, a T-shirt can be seen by everyone, so if you’re weighing up a risqué image or phrase, consider whether you’d like your granny to see it.

“I think all concepts can be used on tees,” says designer Kerry Roper. “That’s probably why they’ve become such a successful part of fashion. They appeal to everyone’s taste. A tee that I dislike may be loved by thousands, even millions of others and vice-versa.”

A big part of successful T-shirt design is understanding your audience. Cute and pink is not hot for 18-year-old ‘sk8r boiz’; if you’re going for the emerging over-30s ‘middle youth’ market, opt for something clever and clean.

If you’re submitting to sites like Threadless or Design By Humans, make sure you understand what kinds of shirts their audiences prefer: bright design puns, or dark, abstract and painterly, for example.

Simplicity has another benefit – it keeps things affordable. Screen-printing is still one of the most popular methods for printing onto T-shirts – and the more colours you use, the more it costs. This raises an age-old design challenge.

“The main challenge of working with a limited colour palette is selecting the right colours,” explains Andrew Gregory. “Unless the design is monochromatic, making it pop off the tee can be really tricky.”

In recent years, more and more designs have featured unusual sizing and positioning of elements – for example, designs that wrap around the side of the tee, or elements that sit on the sleeves or shoulders. This approach has its own set of practical considerations.

“Side prints are a little more challenging because you have to consider what the T-shirt will look like when the wearer has their arm down, so size, colour and boldness all matter,” says Mr Tweak, designer with label Organik Rocka. “Most important, be aware of the seam. The folded fabric will break up your design sometimes causing a slight shift. Take this into account before trying to place an elaborate design in this area.”

Earlier this year John Vingoe set up the clothing label Rapscallion. He explains that before he did so, “I got templates in Photoshop, and bunged my designs on, checking the colours, seeing what works, asking people.”

T-shirt design templates, which are widely available online, will also help you adjust your designs for women’s fitted shirts. These tend to be narrower and more clingy, so templates will help keep your design dimensions tidy. It’s also important to check with your printer that any Lycra that may be blended with the cotton on the women’s version (to make it stretchier) won’t affect the inking.

Again, think about your target audience. Many independent labels take a unisex approach; not all women like figure-hugging tops, so if you pick skin-tight tees for the wrong audience, you might be left with a lot of unsold stock.

T-shirt design is many things. It’s a creative exercise and it’s a money-spinner, but most of all, it’s a calling card. It’s the perfect way to get designs from computer screen to public. Sure it’s great having your name attached to a great bit of illustration on your blog, but wouldn’t it be more interesting to have the endorsement of countless people willing to wear it around in their daily lives? We thought so too.