First you need to get the best iron on transfers. Amy (Mickey) sells them but for obvious reasons can't sell here. They come quickly, hold up well and have complete instructions enclosed. Find her on Meet the DISigners and send her an e-mail. She will send back her website address (I don't believe anyone is supposed to post on the forum).
The HOW TO sticky has tips. Before the transfers arrive you can prep your shirts by washing them....no fabric softener or fabric softener sheets. Then iron so you have a smooth surface to work on.
Amy's transfers are of the dark variety and do NOT require reversing the image. I used them on every color shirt from black to olive green to white!!