As enrollments in computing-related programs continue to rise, computer science departments are increasingly relying on teaching assistants (TAs) to provide additional educational support to students, such as one-on-one tutoring or office hours. Tutoring is more effective with highly trained tutors, but most TAs receive little to no training in pedagogical skills. How might we provide support to TAs working with students one-on-one, especially in remote settings? We propose a just-in-time intervention that shows a tutor actionable teaching tips and relevant information right before they begin an online tutoring session with a student. We conducted a crossover experiment (n = 46) where participants engaged in two tutoring roleplays for an introductory computer science programming task and found that participants demonstrated effective instructional strategies for much longer periods of time after receiving the intervention. We discuss the implications of these findings for both educators looking to support tutors and researchers seeking to build technology for tutors.