After an interview, follow-up is important. Not essential, but a nice touch.
A short e-mail expressing thank you for an interesting discussion is sufficient.
This should be sent on the same day if possible, or next day at the latest.
Do not phone a potential employer afterwards (unless they’re a personal friend or you jointly discovered something personal in common during the interview)!
Also—and please note carefully—a follow-up e-mail is not an opportunity to correct any mistakes that you made in the interview, or to apologise for any mistakes you made, or to clarify any answers you gave in the interview. It’s too late for any of this. Any further comment on such things will make it worse and almost certainly help lose you the job.
An don’t forget—if the interview was arranged through an agent, then phone the agent and discuss the interview with them. They may have already received feedback from the prospective employer—and may have even obtained a decision!