Getting an interview is down to your own ability to sell yourself in your cover letter since this is usually the first thing clients will look at. If you aren't getting ANY interviews and you keep appyling to jobs relevant to your skillset - then I'd suggest revising your profile.
Don't use a generic cover letter, make each one original.
Clients initiate interviews, so if you've applied for a job it could mean:
Focus on your cover letter, try and get the client's attention quickly. Attach some similar work so the client can see your skill.
A lot of people are complaining about this.
They used to get a lot of interviews but once oDesk started hiding applications that they decided did not fit well with the job, the interviews stopped coming.
There's really not much you can do about this. From reading various posts, people (including clients) were complaining that the best freelancers were being hidden.
I don't think oDesk has made any changes so all you can really do is keep on applying and try to make sure that you meet all the requirements for the job.