Give people information, or even be more creative. Get people to share pictures of themselves wearing the t-shirt. Create a community of people who are interested in your product. Get a famous person to wear it and share that picture online. Do something different, do something unique. Show Google that you are different and better than the other search results.
And finally, the other really important bucket is authority. Google wants to show sites that are popular. If they can show the most popular t-shirt seller to people looking to buy t-shirts online, that’s the site they want to show. So you have to convince Google - send them signals that your site is the most popular site for the kind of t-shirts that you sell.
Analysis is the key to SEO – Monitoring your ranking on search engines is key to getting better results. Start by tracking the most important website metrics to set a baseline for your performance. Make small content changes and see if you notice a boost in your site traffic or rankings. Avoid making several unrelated changes simultaneously so you can always keep track of what was responsible for improved performance.
I think ranking in organic listings is a lot about trusted links making trusted pages rank, making trusted links making trusted pages rank ad nauseam for various keywords. Some pages can pass trust to another site; some pages cannot. Some links can. Some cannot. Some links are trusted enough to pass ranking signals to another page. Some are not. YOU NEED LINKS FROM TRUSTED PAGES IF YOU WANT TO RANK AND AVOID PENALTIES & FILTERS.
And so on and so on. The point of this step isn't to come up with your final list of keyword phrases. You just want to end up with a brain dump of phrases you think potential customers might use to search for content related to that particular topic bucket. We'll narrow the lists down later in the process so you don't have something too unwieldy. Once you have your final list, there are several data-driven tools available to you for finding out which keywords you're most likely to rank well for. 

Companies that employ overly aggressive techniques can get their client websites banned from the search results. In 2005, the Wall Street Journal reported on a company, Traffic Power, which allegedly used high-risk techniques and failed to disclose those risks to its clients.[15] Wired magazine reported that the same company sued blogger and SEO Aaron Wall for writing about the ban.[16] Google's Matt Cutts later confirmed that Google did in fact ban Traffic Power and some of its clients.[17]
Your SEO keywords are the keywords and phrases in your web content that make it possible for people to find your site via search engines. A website that is well optimized for search engines "speaks the same language" as its potential visitor base with keywords for SEO that help connect searchers to your site. Keywords are one of the main elements of SEO.