Regardless of how well you word your advert, the majority of applicants will be inappropriate. The only proven solution is to carefully select the medium you use to advertise. For example, if you posted an advert for a Ruby Dev on Monster you would get thousands of replies and be lucky to get one or two decent applicants whereas if the same job was posted on a platform like HN you would have much fewer applicants but a significantly higher calibre of candidate.
Think about the type of people you want to hire. Where are they likely to respond to a job advert?