Just smoke a ton of weed and come up with a couple of designs that you believe are totally imaginative and edgy when really you ripped them off from a few artsy Instagram posts you saw a few days ago. Then, silkscreen them onto some shirts. If you give your clients options like black or white, tank top or baby tee, that's like, a bunch of t-shirt options you have to sell already. Obviously, jack up the price to an insane amount of money. Justify your pricing by saying the t-shirt is made of 100% cotton that is handpicked from a field in *insert exotic location here.* Have your social media be abundant with photos of your models who have the same waistline as the small foreign children who make your t-shirts for fifty cents an hour. Create a douchey mission statement that makes it seem like your line isn't about fashion, it's about an innovative movement that can change the world (when really, it's just a F*CKING T-SHIRT LINE).