Learning to write and speak effectively is an essential part of becoming a successful researcher. Unfortunately, many researchers, especially junior researchers, struggle to communicate their ideas clearly, in large part because they have a hard time putting themselves in the shoes of their audience. In this talk, I will present time-tested principles of clear communication that will help you write more accessible papers and give more engaging presentations. Unlike such famous advice as “Be clear” or “Omit needless words”, the principles I present will be constructive: you can easily check whether your paper or presentation satisfies them, and if it does not, the principles suggest concrete ways to improve it. The material for this talk was developed together with my partner Rose Hoberman, who has been helping students improve their writing and speaking skills at MPI-SWS for the past 17 years.