Full-time game testing is a rough job. Unlike casual testing (such as open beta where you can generally run around and play the game at your leisure), full-time game testing goes more in-depth to a tedious degree. A real basic example is you could be assigned to test the layout of a zone; this may entail starting at square 1x1, moving to square 1x2, 1x3, et cetera, and your job would be to make sure that the world geometry is fine (ranging from finding invisible holes/barriers to noting glitchy textures that only occur at certain angles). Unlike casual testing where feedback is optional, you'll likely be required to write out detailed reports of bugs. Sometimes this type of job is part-time, but it could be full-time, meaning you better be able to sit in front of a computer for 8-hours a day and maintain focus. During crunch time before the actual release, you may be working overtime (60-80 hour weeks).
If you're trying to get an actual job in the field, you'll want to tout your analytical and communicative skills. As well, if you've ever tested previous games (as a casual tester, even), list those that you can (without breaching NDAs). If the company you're interested in is having an open-beta, get in and give proper feedback (unlike some people who just play around for the hell of it). Finally, if you get an interview, be prepared to give examples of well-made games you admire and why.
That's all I can think of off the top of my head. I'm not an industry person myself, but I have friends in the industry.