You should first determine what skillsets you would like the IMO to have, and whether the IMO should be a specialist or a generalist. There are several pages of the IM Unit Management - People section of the IM Toolbox can help you with that.
When advertising the position, depending on the skillsets that you would like to focus on, use one of the job descriptions that were developed by the Global IM Functional Team (GIFT) and cleared by human resources:
Feel free to contact Field Information Services (FIS) to help you with screening, testing and interviews. Remember that if you are recruiting against a JO (as opposed to a TJO), all candidates recommended for the position will be added to the IMO roster.