An op-ed should be understandable to a general reader. In other words, if the reader needs to have a PhD in Middle East history to understand what you are writing about, it is unlikely to be printed. Newspapers like op-eds from members of the local community who have some personal stake in the issue. Simply having a personal connection to the issue or a long-standing interest is often enough. Most important is to have a well-written and compelling article.
Every newspaper has different guidelines for accepting an op-ed.
Some accept email, others only faxes. The best way is to call the newspaper up and ask for the op-ed editor and ask what the guidelines are. If you submit your op-ed by email or fax, follow up with a phone call to make sure it was received and to ask when you can expect an answer. Disappointment is an integral part of trying to get an op-ed printed. In our experience, MOST of our op-eds are rejected.