Wikipedia and blogs have the best keywords. Target words like gift, birthday and apparel in your bullet points. Keep your listings under 250 characters. Price your shirts low until you get that initial sale then raise it up a couple dollars. Don't describe everything going on in the design. Dudes be havin titles like "Dabbing Persian Cat Doing The Milly Rock Premium Novelty Shirt." Use 3 words max to describe the design concept and that's it. Use the rest of that space for keywords related to your niche. The word "T-Shirt" covers tshirt, t shirt and shirt. Don't be repetitive. You should only be using the main keyword more than once in your brand, title and bullet points. Any other keyword? Only use it once or use a variation of it.