[Frazmatazz]

The very fact that they serve many clients gives the service a good view on what generates increased response rates.

I once scraped a bunch of job postings and did a simple word frequency count. Just eyeballing the list, I picked out a few of the most commonly mentioned techs and skills. By just rewording a few of my resume entries, it seemed to increase my response rate by quite a bit.

For example, in the description of one project I added "using JSON". It wasn't particularly important to that project that the exchange format used was JSON, but apparently many of those doing hiring are seeing fit to include that in their searches.