For photographs printed onto a garment a minimum of 300dpi. and send as a jpg or png file.
If you have a design in a vector based program like Illustrator, then flatten transparency and convert everything to outlines, curves, Save them as a PDF or EPS file.
If you are using a non-vector based program like Photoshop then please save the design as a high quality PDF.
If you are unsure of any of the above just get in touch and we will advise you from there what to do.