I moved somehow from biophysics to a mixed team where we usually publish in TCS journal / conferences. For getting funding, in the European country where I live, it is advisable to show in your CV that I have refereed papers or conferences on these fields. I have more than 30 publications but never really thought about this. So my question goes, how can I become referee in these cases?
Generally, you are invited to be a referee because the editor knows you or your work or he/she finds you because the paper under review cites your work or is in the same field as your work (perhaps via a google search).
Of course, if you are on the PC of a conference, you get to review loads of papers. You get on the PC by being invited, generally because you are either an old hand in the field or an up and coming star (or a friend/(ex-)colleague of the PC chair).
If you are a student or post-doc, then you should get to do some reviewing if your supervisor/boss/colleague/etc is on the PC of a conference.
In short, you need to be known or linked with someone who is known. Or alternatively you could ask a colleague whether you could review some papers for him/her next time he/she is on a PC.