I've been reading the forums a lot and one of the big themes I see is business owners needing ideas for marketing.
Here are some ideas that helped me.
Sponsor a very small roller derby team.
I got into tshirts and other branded things when my roller derby team had zero money for jerseys, merchandise, or even flyers to place in windows about upcoming games. So I researched, bought a cheap chinese heat press as big as I could afford then (15x15 and it's still working amazingly well) and found Coastal Business supply as my heat transfer supplier. Went to Hobby Lobby and got some shirts in green, black and white and made our merch. Girls brought their own tank tops and I would heat press numbers on the back. Then I got a Cameo cutter and started doing my thing. Roller derby girls pay a monthly dues fee in order to pay for skate time, they are fully internally funded and only make money when people come to see them play. If you offer to help a derby team by making the merch and get paid when merch sells, you help them and they tell all their friends about you.
Fall baseball is in full swing everywhere you can play in the fall. Go to the local fields and hand out business cards. Take a few sample shirts in cotton and poly with a fake team name on the front and a name/number set up on the back so coaches can see the end result. Little Leagues are also self funded, parents pay for their kids to play and all field rental, umpire payments, uniforms, advertising and the like comes from those funds. If you can do the same job for $2 less each player, it means a lot to the league to save that money. My biggest client is the local Little League. 30 teams of 14 plus 3 coaches each team, plus spirit wear for parents, shirts for volunteers, etc. Worth the $18K a year to save that league $3 a kid each season, Spring and Fall. Do decals of a baseball (or football, or lacross stick, gymnast) with the player number and name.
Use your car windows
My daughters car windows, rear and the two non-opening side windows are an advertising tool for me. Her back window is outlined in a multi-colored floral pattern with leaves and bees and a couple ladybugs. Along the bottom, it says "Want a window like this? Call Imagesinthewind Studios at 303-XXX-XXXX" Her side windows have other fun decals, and one has "Imagesinthewind Studios, Custom Work, Decals, Lettering, T-Shirts, Small Runs Welcome!" She parks in the college parking lot and goes to school 3 days a week from 8 to 5. Free advertising. We change it up when the 'new thing' comes up. Like during the election season, one side was dedicated to our candidate. Nothing for the other...I will not sell out like that. I don't play both sides. If you have a best friend with a kid in college, try this out. Costs you sign vinyl and time. I get 3-5 orders a month from her car. Including a volleyball team that all wanted a ball with their name and number around it for their car windows.
Give away decals with t-shirts. Stickers work. All I can say. I send a cute decal, single color, with some flowers and the text 'Be Kind' with every order. I cut a bunch out, different colors of sign vinyl (Oracal 651) and toss one in with each order. Costs me about .25 and gains me soooo much. Even if it's not in money, that .25 decal gained me good will.
Give away small 1.5 x 1.5 decals with your business cards. Peace sign, hibiscus flower, tiki face, angel, pot leaf, tribal or celtic design, eye of Horus, snowflakes, cat face, yin yang, Om symbol, you get the idea. Make them all white so if the receiver puts it on the car window, it shows up. Cost to you is small.
But you have to go where the customer is. You have to go see a roller derby bout (game). You have to go watch a Little League baseball game, you have to go to the car show, the festival in the park, the parking lot at Home Depot (ask that plumber if he needs someone to redo that peeling lettering on his truck and why not a few new t-shirts for a fresher look).
Customers are better found when you go to them. Don't sit back behind your computer and try and WILL them to find you.
Lastly, if you're on this forum for information before you've taken the dive, I cannot press upon you enough how important a business plan is. Learning how to market is the hardest part and should take you months of research. Asking after you've spent all your hard earned on machines and software and THEN about how to find customers is backward. You first need to know how you'll find the business, then you will need to decide your niche. You can't be everything to everybody, so decide what kind of items you'll sell and what you need to do that. Know how much of each sale will pay YOU and how much will go into replenishing stock and how much will go into a savings account for the new bigger heat press you'll need someday, etc.
I started out small, and grew slowly. I'm about to branch into dye sub, mostly because I want to try it. I've got enough clients that when I'm set up, I can send emails and samples to bigger past spenders and ask what new things we can do together.
Sorry, ranting now. Good luck and I hope this helps you think about ways to look outside your box.