To custom print a t-shirt, start by choosing a design or creating your own. Consider the colors, size, and placement of the design on the shirt. Next, select a printing method that suits your design and budget, such as screen printing, heat transfer, or direct-to-garment printing. Prepare your design file according to the printer's specifications, ensuring it is the right size and format. Then, choose the type and color of t-shirt you want to print on. Place your order with a printing company, providing them with your design and shirt preferences. Once the shirts are printed, inspect them for quality and accuracy before distributing or wearing them.