The COVID-19 pandemic meant a move to emergency remote teaching for many university students around March 2020. Two months later, we undertook an online survey to ascertain experiences of university mathematics lecturers. We received responses from 257 mathematics lecturers from 29 countries. In this paper, we consider their responses when asked what advice they would give to colleagues, based on their experience of online teaching to date. We gather their collective wisdom under a number of themes, including technology options, effective online teaching approaches, and supporting students, as well as reducing stress and setting realistic expectations for both learners and teachers.