Generally the OCS PCs would tell you that only top XX% gets selected for Recon roles and so on so forth. How many of us who were there actually dare to say they fall into that particular percentile?

But what I can conclude so far is a good sense of direction and good navigation skills are enough to land you the job. It helps too if there are vacancies and you're not posted to Wings reputed for churning out people destined for support vocations (ie QM, DyS).
All these were before the new Int Officer vocation came into play. Last I heard, only regulars in that vocation have priorities to the job.