I read the first four Earthsea books in my adolescence, and in the last several years have been reading Le Guin's adult works and re-reading Earthsea.
I would say that there is no strict order that you need to read them in aside from reading Earthsea novels chronologically. You do not need to read any of the Earthsea short stories before starting with A Wizard of Earthsea.
The Hainish cycle novels may be nice to read in the order they were written, especially if you're reading with the intention of understanding Le Guin's development as a writer, but from a story perspective, there's not a lot of strong relationships between the books. (Full Disclosure: out of the novels, I have currently read only Left Hand, Dispossessed, Four Ways, and Telling). The only caveat I have is that you should try to read the short story "Old Music and the Slave Women" (in Birthday of the World) after you have read Four Ways to Forgiveness.
I also don't see any reason to specifically read Earthsea before or after her adult works. Earthsea is completely separate from everything else she wrote, so you could read it before, during, or after your other reading.
In summary, roughly chronological order is probably good, but don't get too worried if Left Hand of Darkness is checked out of the library on your next trip and you have to start with The Dispossessed.