Nacho... I've hired quite a few people, so here's the few suggestions that I can provide for you...
For one, be truthful the whole way. A good interviewer will sniff out discrepancies, so trying to "hype" yourself up during the interview or amplifying things sitting on your resume will probably fuck you in the end. With adult, I wouldn't mention it unless you get the sense that they're looking for someone with the ability to serve those types of clients.
Be to-the-point. Don't beat around the bush, stick it right in. Most companies today (especially small firms) are looking for decisive people that don't need to consult with their boss before taking a leak.
When talking about SEO, make sure to justify everything that you've done or mentioned during the interview and on your resume. Classic SEO rules apply, such as never guaranteeing high ranking, or recognizing that the SE algos are always changing and you regularly stay on top of the latest SEO commentators.
CPC, SEM, Long & Short tail Keyword harvesting, etc., you should really point out a few success stories, as well as the scale & scope of projects you've taken on. You will SERIOUSLY improve your chances of getting a job by bringing in printouts of a few of your campaign summaries (be sure to black out any information that you don't want to disclose).
The best thing that you can do is have DOCUMENTED EVIDENCE of everything that you claim that you can do. Don't count on there being a computer in the room, so print everything out.
Good luck bro!