Firstly, you will need your Bishop's approval. However, before that (sorry if that is ironic), you will need to make sure that you have enough people in the area who would like to be in a mission. Enough people? Hmm...
Here is a link that has some info. Quoting from it (member David):
Here is how most OCA missions have been established in our diocese for the last twenty years or so.
- Secure a core group to explore starting a mission (usually 2-5 families/individuals) that are Orthodox
- Contact your bishop, letting him know of your desire to start a mission in your area.
- If the bishop approves, he will give you permission to start holding reader's services. Perhaps one or more of the starting members will be tonsured a reader if a member in good standing at their last parish.
- Once you have secured a place to meet and have had reader's services for a month or two, the local dean and/or bishop will arrange to have supply priests hold a liturgy at the mission at least once a month. At this point the mission usually receives it's name.
- After showing enough growth that demonstrates that the community has the potential to evangelise their local area and support a priest and his family either a priest will be assigned to the mission or one of the mission families will go to seminary.
Really, though, this type of question should be asked of a Priest (or Bishop :)), not of online strangers... :)