If you’re working with a recruiter, the first thing to do is touch base with him/her asap after your interview. Share your thoughts on how the interivew went, was the job in line with what you were told by the recruiter and the job description, how did the interviewer(s) leave off with you, and are you intersted in moving forward should the firm want to bring you back. It’s become a standard practice to sent a "thank you email" to the interviewer(s), generally keep this "short & sweet", concise and professional, WITHOUT any typos!
Don’t neccessarily expect feedback from the firm or the recuriter right away, and check with the recruiter after a few days if you haven’t heard anything. Don’t be discouraged if you don’t hear feedback as this is quite common these days.