What's your top tip for doing well at interview?

Come prepared. While it may sound obvious, being prepared is one of the most important factors of a good interview. This means:
1) reading up on the company and what it does.
2) structuring your resume or portfolio to fit the job description.
3) anticipating interviewer's questions and practicing your responses.
4) reviewing technical material to answer technical questions.
5) etc

Being prepared not only puts forth a good impression, it also puts you in a state of confidence as you begin the interview. Ultimately, an interview is a process for the company to know more about you and to see if you will be a good fit for the company. So come prepared and just be yourself!

All the best!