how can you customize a t shirt

Ok now how can you customize a t shirt from Where will you go and whom you will contact to customize or design or imprint? There are many merchants in the market who offer customize t shirt to the people. But they put higher price tag for those custom t shirts. If also they provide for higher price tags but the quality of the t shirts are not up to the mark that we expect. There are lots of things to take into consideration before applying for customizing a t shirt. Some of those are cloth type, cloth material, design work and imprint quality.