Merch by Amazon and Spreadshirt are two popular platforms that allow you to design and sell t-shirts. Merch by Amazon is a print-on-demand service, which means that you don't have to worry about inventory or shipping. Spreadshirt is a self-publishing platform, which gives you more control over the design and production of your t-shirts.

If you're interested in starting your own t-shirt business, here are 10 tips to get you started:

1. Choose a niche. When you're first starting out, it's best to focus on a specific niche. This will help you narrow down your target audience and make it easier to come up with high-quality designs.
2. Do your research. Before you start designing, it's important to do your research and find out what kind of designs are popular in your niche. You can use tools like Google Trends and Pinterest to help you with this.
3. Create high-quality designs. Your designs are the most important part of your business, so it's important to make sure they're high-quality. Use high-resolution images and fonts, and make sure your designs are visually appealing.
4. Choose the right keywords. When you're uploading your designs to Merch or Spreadshirt, it's important to choose the right keywords. This will help people find your designs when they're searching for t-shirts online.
5. Promote your products. Once you've uploaded your designs, it's important to promote them. You can do this by sharing them on social media, running ads, or submitting them to t-shirt marketplaces.
6. Be patient. It takes time to build a successful t-shirt business. Don't get discouraged if you don't start seeing sales right away. Just keep designing great t-shirts and promoting your products, and eventually you'll start to see results.
7. Use a variety of design styles. Don't just stick to one type of design. Experiment with different styles and see what works best for you.
8. Collaborate with other designers. Collaborating with other designers is a great way to get new ideas and expand your reach.
9. Attend t-shirt trade shows. Attending t-shirt trade shows is a great way to network with other designers and learn about the latest trends.
10. Stay up-to-date on the latest trends. The t-shirt industry is constantly evolving, so it's important to stay up-to-date on the latest trends. You can do this by reading industry blogs, attending trade shows, and following other designers on social media.

By following these tips, you can increase your chances of success with Merch by Amazon or Spreadshirt.