When you think you are getting close to wanting to serve, contact the Mission President where you want to serve and have a discussion with him about when and how you might enjoy serving.

It does not matter if you already have a relationship with him; start one.

If a Mission President requests that a couple serve in his mission and the couple indicates on their application that they want to serve in X mission by invitation of the MP, there is about a 95% chance that will happen.

Every MP is desperate to have couples serving in their mission and it does not always have to be in the office.

We served with six couples doing different things; one chose proselyting, one served in the office (by choice), two were MLS (Member and Leader Support); one served in the Temple; one served as medical support.

The Missionary Department will tell you that couple missionary assignments are still subject to "inspiration" by the member of the Q12 making the call, but, 95% go where they want if the MP requests them.

Sign me up for middle of nowhere Chile. My wife and I both served there when young.