Can you give me insight on what you use for research?
I'll let 2RAWW chime in on what he uses but here is everything you need to get going:
1. Download the Chrome extension: DS Amazon Quick View
This will allow you to, after doing a search on Amazon, quickly scroll down the page and look at the BSR (best sellers rank) of each shirt without having to click on each indivual design.
If you aren't already, get familiar with BSR. It is the key to understanding how successful a shirt is selling.
Outside of finding ideas on Reddit, Pinterest, Google, Google Trends, Twitter, Instagram, getting out and about, staying up on the latest trends and pop culture news, etc..
2. Amazon.com (which will show you all shirts mashed together) and merchresearch.com (which will only show you Merch by Amazon shirts). Both are free and both are where I do the majority of my research.
Just go to Amazon.com and enter search terms and see whats out there. See where there is a demand. Amazon.com will show you all shirts, not just Merch shirts. Amazon.com sells their own stuff, as well as allows 3rd party sellers to sell stuff too. All of it can be found mashed together when you search for things via the site. You can get an idea of whats selling, based on the BSR. If there is no BSR it has yet to sell. The lower the BSR the better it is selling.
http://www.merchresearch.com is dope, it will only pull the Merch shirts that are on Amazon so you can see the entirety of whats out there.To see every shirt on Merch don't put any search terms, just hit enter. It will show show you, in order, the most successful shirt, on down the line.You can also search for a specific term which will show you, in order of sales, the shirts in that particular niche.
Here is a screenshot of the first page of Merch shirts, after hitting enter on merchresearch, with the DS Amazon Quick View extension showing you the BSR's.
The first couple shirts have BSR's of 82, 93, 208. They are each selling hundreds a day.