You should first find what is max resolution of printer you will be using.
A lot of the older printers are 300 dpi, newer ones range from 600-2400 or more.
Also, don't forgets to add a border if you are stretching to frame or just matte.
I usually send out to service like redbubble or deviantart because they have nice printers and can color manage (also they have the frames)