To ensure successful conference calls, there are three things participants should avoid: 1) Multitasking, as it leads to drops in productivity and IQ. Participants should focus solely on the meeting. 2) Forgetting to mute oneself, as it can allow interruptions like barking dogs or eating chips to disrupt the call. 3) Coming unprepared, which risks falling behind or awkward interruptions, especially without visual cues over audio-only calls. Preparing ensures positive contributions.